I agree that God has progressively revealed His plan of redemption throughout the Bible. However, that is different from saying something like it once was in accordance with God's righteousness to help the poor, but not that is no longer the case, or it once was sinful to commit murder, but now that is no longer the case. God's righteousness is eternal and unchanging, so any instructions that God has ever given for how to act in accordance with His righteousness and to refrain from sin are also eternal and unchanging and will always be valid regardless of which covenant we are under, even for those who are not in a covenant relationship with God.
In pretending that Paul taught that it was necessary to obey the law, you are wresting his words, and in challenging his authority as an Apostle of Jesus Christ, you are denying that all scripture is given by inspiration of God.
1 O foolish Galatians, who hath bewitched you, that ye should not obey the truth, before whose eyes Jesus Christ hath been evidently set forth, crucified among you? 2 This only would I learn of you, Received ye the Spirit by the works of the law, or by the hearing of faith? 3 Are ye so foolish? having begun in the Spirit, are ye now made perfect by the flesh? 4 Have ye suffered so many things in vain? if
it be yet in vain. 5 He therefore that ministereth to you the Spirit, and worketh miracles among you,
doeth he it by the works of the law, or by the hearing of faith? 6 Even as Abraham believed God, and it was accounted to him for righteousness.
Galatians 3:1-6
10 For as many as are of the works of the law are under the curse: for it is written, Cursed
is every one that continueth not in all things which are written in the book of the law to do them. 11 But that no man is justified by the law in the sight of God,
it is evident: for, The just shall live by faith. 12 And the law is not of faith: but, The man that doeth them shall live in them. 13 Christ hath redeemed us from the curse of the law, being made a curse for us: for it is written, Cursed
is every one that hangeth on a tree: 14 That the blessing of Abraham might come on the Gentiles through Jesus Christ; that we might receive the promise of the Spirit through faith.
Galatians 3:10-14
19 Wherefore then
serveth the law? It was added because of transgressions, till the seed should come to whom the promise was made;
and it was ordained by angels in the hand of a mediator. 20 Now a mediator is not
a mediator of one, but God is one. 21
Is the law then against the promises of God? God forbid: for if there had been a law given which could have given life, verily righteousness should have been by the law. 22 But the scripture hath concluded all under sin, that the promise by faith of Jesus Christ might be given to them that believe. 23 But before faith came, we were kept under the law, shut up unto the faith which should afterwards be revealed. 24 Wherefore the law was our schoolmaster
to bring us unto Christ, that we might be justified by faith. 25 But after that faith is come, we are no longer under a schoolmaster.
Galatians 3:19-25
9 But now, after that ye have known God, or rather are known of God, how turn ye again to the weak and beggarly elements, whereunto ye desire again to be in bondage? 10 Ye observe days, and months, and times, and years. 11 I am afraid of you, lest I have bestowed upon you labour in vain.
Galatians 4:9-11
21 Tell me, ye that desire to be under the law, do ye not hear the law? 22 For it is written, that Abraham had two sons, the one by a bondmaid, the other by a freewoman. 23 But he
who was of the bondwoman was born after the flesh; but he of the freewoman
was by promise. 24 Which things are an allegory: for these are the two covenants; the one from the mount Sinai, which gendereth to bondage, which is Agar. 25 For this Agar is mount Sinai in Arabia, and answereth to Jerusalem which now is, and is in bondage with her children. 26 But Jerusalem which is above is free, which is the mother of us all. 27 For it is written, Rejoice,
thou barren that bearest not; break forth and cry, thou that travailest not: for the desolate hath many more children than she which hath an husband. 28 Now we, brethren, as Isaac was, are the children of promise. 29 But as then he that was born after the flesh persecuted him
that was born after the Spirit, even so
it is now. 30 Nevertheless what saith the scripture? Cast out the bondwoman and her son: for the son of the bondwoman shall not be heir with the son of the freewoman. 31 So then, brethren, we are not children of the bondwoman, but of the free.
Galatians 4:21-31
1 Stand fast therefore in the liberty wherewith Christ hath made us free, and be not entangled again with the yoke of bondage. 2 Behold, I Paul say unto you, that if ye be circumcised, Christ shall profit you nothing. 3 For I testify again to every man that is circumcised, that he is a debtor to do the whole law. 4 Christ is become of no effect unto you, whosoever of you are justified by the law; ye are fallen from grace. 5 For we through the Spirit wait for the hope of righteousness by faith. 6 For in Jesus Christ neither circumcision availeth any thing, nor uncircumcision; but faith which worketh by love. 7 Ye did run well; who did hinder you that ye should not obey the truth? 8 This persuasion
cometh not of him that calleth you.
Galatians 5:1-8
I have simply answered you with the exact words of scripture. But this entire discussion of entirely off the subject for this thread, which is not whether or not Dispensationalism is correct, but how long it has been taught.