Just out of curiosity, I did some searching on the internet, and found this:
Week - Wikipedia
The summary is that the seven day week appears to be a middle eastern thing, which then spread to other places. It doesn't seem to be a particularly godly practice, from a purely historical point of view.
(I didn't read the entire Wikipedia article, so if someone knows of other ancient cultures that did a 7-Day week, I'm interested.)
Bottom line: I couldn't find anything about godly people who don't have the scriptures celebrating the seventh day,
so it doesn't seem to be something written on their hearts as Romans talks about.
Early Church Fathers who lived before the Council of Nicaea comment on the Sabbath:
Ignatius of Antioch
If, therefore, those who were brought up in the ancient order of things have come to the possession of a new hope, no longer observing the Sabbath, but living in the observance of the Lord’s Day, on which also our life has sprung up again by Him and by His death—whom some deny, by which mystery we have obtained faith, and therefore endure, that we may be found the disciples of Jesus Christ, our only Master(Letter to the Magnesians(shorter) Chapter IX.—Let us live with Christ [A.D. 110]).
During the Sabbath He continued under the earth in the tomb in which Joseph of Arimathæa had laid Him. At the dawning of the Lord’s day He arose from the dead, according to what was spoken by Himself, “As Jonah was three days and three nights in the whale’s belly, so shall the Son of man also be three days and three nights in the heart of the earth.” The day of the preparation, then, comprises the passion; the Sabbath embraces the burial; the Lord’s Day contains the resurrection(The Epistle of Ignatius to the Trallians Longer Versions. Chapter IX.—Reference to the history of Christ.)
Justin Martyr
The Lawgiver is present, yet you do not see Him; to the poor the Gospel is preached, the blind see, yet you do not understand. You have now need of a second circumcision, though you glory greatly in the flesh. The new law requires you to keep perpetual sabbath, and you, because you are idle for one day, suppose you are pious, not discerning why this has been commanded you: and if you eat unleavened bread, you say the will of God has been fulfilled. The Lord our God does not take pleasure in such observances: if there is any perjured person or a thief among you, let him cease to be so; if any adulterer, let him repent; then he has kept the sweet and true sabbaths of God. If any one has impure hands, let him wash and be pure.(Dialogue with Trypho the Jew Chapter XII.—The Jews violate the eternal law, and interpret ill that of Moses.)
For we too would observe the fleshly circumcision, and the Sabbaths, and in short all the feasts, if we did not know for what reason they were enjoined you,—namely, on account of your transgressions and the hardness of your hearts. For if we patiently endure all things contrived against us by wicked men and demons, so that even amid cruelties unutterable, death and torments, we pray for mercy to those who inflict such things upon us, and do not wish to give the least retort to any one, even as the new Lawgiver commanded us: how is it, Trypho, that we would not observe those rites which do not harm us, —I speak of fleshly circumcision, and Sabbaths, and feasts?(Dialogue with Trypho the Jew Chapter XVIII.—Christians would observe the law, if they did not know why it was instituted. [A.D. 155]).
And we afterwards continually remind each other of these things. And the wealthy among us help the needy; and we always keep together; and for all things wherewith we are supplied, we bless the Maker of all through His Son Jesus Christ, and through the Holy Ghost. And on the day called Sunday,1 all who live in cities or in the country gather together to one place, and the memoirs of the apostles or the writings of the prophets are read, as long as time permits; then, when the reader has ceased, the president verbally instructs, and exhorts to the imitation of these good things. Then we all rise together and pray, and, as we before said, when our prayer is ended, bread and wine and water are brought, and the president in like manner offers prayers and thanksgivings, according to his ability, and the people assent, saying Amen; and there is a distribution to each, and a participation of that over which thanks have been given, and to those who are absent a portion is sent by the deacons. And they who are well to do, and willing, give what each thinks fit; and what is collected is deposited with the president, who succours the orphans and widows and those who, through sickness or any other cause, are in want, and those who are in bonds and the strangers sojourning among us, and in a word takes care of all who are in need. But Sunday is the day on which we all hold our common assembly, because it is the first day on which God, having wrought a change in the darkness and matter, made the world; and Jesus Christ our Saviour on the same day rose from the dead. For He was crucified on the day before that of Saturn (Saturday); and on the day after that of Saturn, which is the day of the Sun, having appeared to His apostles and disciples, He taught them these things, which we have submitted to you also for your consideration.(First Apology Chapter LXVII.—Weekly worship of the Christians. [A.D. 155]).
“Wherefore, Trypho, I will proclaim to you, and to those who wish to become proselytes, the divine message which I heard from that man. Do you see that the elements are not idle, and keep no Sabbaths? Remain as you were born. For if there was no need of circumcision before Abraham, or of the observance of Sabbaths, of feasts and sacrifices, before Moses; no more need is there of them now, after that, according to the will of God, Jesus Christ the Son of God has been born without sin, of a virgin sprung from the stock of Abraham. For when Abraham himself was in uncircumcision, he was justified and blessed by reason of the faith which he reposed in God, as the Scripture tells. Moreover, the Scriptures and the facts themselves compel us to admit that He received circumcision for a sign, and not for righteousness.(The Second Apology of Justin for the Christians Addressed to the Roman Senate. Chapter XXIII.—The opinion of the Jews regarding the law does an injury to God.)
“As, then, circumcision began with Abraham, and the Sabbath and sacrifices and offerings and feasts with Moses, and it has been proved they were enjoined on account of the hardness of your people’s heart, so it was necessary, in accordance with the Father’s will, that they should have an end in Him who was born of a virgin, of the family of Abraham and tribe of Judah, and of David; in Christ the Son of God, who was proclaimed as about to come to all the world, to be the everlasting law and the everlasting covenant, even as the forementioned prophecies show.(The Second Apology of Justin for the Christians Addressed to the Roman Senate. Chapter XLIII.—He concludes that the law had an end in Christ, who was born of the Virgin.)
Tertullian
“[L]et him who contends that the Sabbath is still to be observed as a balm of salvation, and circumcision on the eighth day . . . teach us that, for the time past, righteous men kept the Sabbath or practiced circumcision, and were thus rendered ‘friends of God.’ For if circumcision purges a man, since God made Adam uncircumcised, why did he not circumcise him, even after his sinning, if circumcision purges? . . . Therefore, since God originated Adam uncircumcised and unobservant of the Sabbath, consequently his offspring also, Abel, offering him sacrifices, uncircumcised and unobservant of the Sabbath, was by him [God] commended [Gen. 4:1–7, Heb. 11:4]. . . . Noah also, uncircumcised—yes, and unobservant of the Sabbath—God freed from the deluge. For Enoch too, most righteous man, uncircumcised and unobservant of the Sabbath, he translated from this world, who did not first taste death in order that, being a candidate for eternal life, he might show us that we also may, without the burden of the law of Moses, please God”(An Answer to the Jews Chapter II.—The Law Anterior to Moses. [A.D. 203]).
It follows, accordingly, that, in so far as the abolition of carnal circumcision and of the old law is demonstrated as having been consummated at its specific times, so also the observance of the Sabbath is demonstrated to have been temporary.For the Jews say, that from the beginning God sanctified the seventh day, by resting on it from all His works which He made; and that thence it was, likewise, that Moses said to the People: “Remember the day of the sabbaths, to sanctify it: every servile work ye shall not do therein, except what pertaineth unto life.” Whence we (Christians) understand that we still more ought to observe a sabbath from all “servile work” always, and not only every seventh day, but through all time. And through this arises the question for us, what sabbath God willed us to keep? For the Scriptures point to a sabbath eternal and a sabbath temporal. For Isaiah the prophet says, “Your sabbaths my soul hateth;” and in another place he says, “My sabbaths ye have profaned.”9 Whence we discern that the temporal sabbath is human, and the eternal sabbath is accounted divine; concerning which He predicts through Isaiah: “And there shall be,” He says, “month after month, and day after day, and sabbath after sabbath; and all flesh shall come to adore in Jerusalem, saith the Lord;” which we understand to have been fulfilled in the times of Christ, when “all flesh”—that is, every nation—“came to adore in Jerusalem” God the Father, through Jesus Christ His Son, as was predicted through the prophet: “Behold, proselytes through me shall go unto Thee.” Thus, therefore, before this temporal sabbath, there was withal an eternal sabbath foreshown and foretold; just as before the carnal circumcision there was withal a spiritual circumcision foreshown. In short, let them teach us, as we have already premised, that Adam observed the sabbath; or that Abel, when offering to God a holy victim, pleased Him by a religious reverence for the sabbath; or that Enoch, when translated, had been a keeper of the sabbath; or that Noah the ark-builder observed, on account of the deluge, an immense sabbath; or that Abraham, in observance of the sabbath, offered Isaac his son; or that Melchizedek in his priesthood received the law of the sabbath
But the Jews are sure to say, that ever since this precept was given through Moses, the observance has been binding. Manifest accordingly it is, that the precept was not eternal nor spiritual, but temporary, which would one day cease. In short, so true is it that it is not in the exemption from work of the sabbath—that is, of the seventh day—that the celebration of this solemnity is to consist, that Joshua the son of Nun, at the time that he was reducing the city Jericho by war, stated that he had received from God a precept to order the People that priests should carry the ark of the testament of God seven days, making the circuit of the city; and thus, when the seventh day’s circuit had been performed, the walls of the city would spontaneously fall. Which was so done; and when the space of the seventh day was finished, just as was predicted, down fell the walls of the city. Whence it is manifestly shown, that in the number of the seven days there intervened a sabbath-day. For seven days, whencesoever they may have commenced, must necessarily include within them a sabbath-day; on which day not only must the priests have worked, but the city must have been made a prey by the edge of the sword by all the people of Israel. Nor is it doubtful that they “wrought servile work,” when, in obedience to God’s precept, they drave the preys of war. For in the times of the Maccabees, too, they did bravely in fighting on the sabbaths, and routed their foreign foes, and recalled the law of their fathers to the primitive style of life by fighting on the sabbaths. Nor should I think it was any other law which they thus vindicated, than the one in which they remembered the existence of the prescript touching “the day of the sabbaths.” Whence it is manifest that the force of such precepts was temporary, and respected the necessity of present circumstances; and that it was not with a view to its observance in perpetuity that God formerly gave them such a law.(An Answer to the Jews Chapter IV.—Of the Observance of the Sabbath.)
Therefore, since it is manifest that a sabbath temporal was shown, and a sabbath eternal foretold; a circumcision carnal foretold, and a circumcision spiritual pre-indicated; a law temporal and a law eternal formally declared; sacrifices carnal and sacrifices spiritual foreshown; it follows that, after all these precepts had been given carnally, in time preceding, to the people Israel, there was to supervene a time whereat the precepts of the ancient Law and of the old ceremonies would cease, and the promise3 of the new law, and the recognition of spiritual sacrifices, and the promise of the New Testament, supervene;4 while the light from on high would beam upon us who were sitting in darkness, and were being detained in the shadow of death.5 And so there is incumbent on us a necessity6 binding us, since we have premised that a new law was predicted by the prophets, and that not such as had been already given to their fathers at the time when He led them forth from the land of Egypt,7 to show and prove, on the one hand, that that old Law has ceased, and on the other, that the promised new law is now in operation.
And, indeed, first we must inquire whether there be expected a giver of the new law, and an heir of the new testament, and a priest of the new sacrifices, and a purger of the new circumcision, and an observer of the eternal sabbath, to suppress the old law, and institute the new testament, and offer the new sacrifices, and repress the ancient ceremonies, and suppress8 the old circumcision together with its own sabbath, and announce the new kingdom which is not corruptible. Inquire, I say, we must, whether this giver of the new law, observer of the spiritual sabbath, priest of the eternal sacrifices, eternal ruler of the eternal kingdom, be come or no: that, if he is already come, service may have to be rendered him; if he is not yet come, he may have to be awaited, until by his advent it be manifest that the old Law’s precepts are suppressed, and that the beginnings of the new law ought to arise. And, primarily, we must lay it down that the ancient Law and the prophets could not have ceased, unless He were come who was constantly announced, through the same Law and through the same prophets, as to come.(An Answer to the Jews Chapter VI.—Of the Abolition and the Abolisher of the Old Law. [A.D. 203]).
But you, many of you, also under pretence sometimes of worshipping the heavenly bodies, move your lips in the direction of the sunrise. In the same way, if we devote Sun-day to rejoicing, from a far different reason than Sun-worship, we have some resemblance to those of you who devote the day of Saturn to ease and luxury, though they too go far away from Jewish ways, of which indeed they are ignorant.(Apology Chapter XVI.)
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If that's the case, I don't think there's any real disagreement between us, them 
