Actually, as has been touched on, as far as scripture is concerned, there are only two times mentioned with regard to anybody getting together on the first (day) of the week - John 20:19 and Acts 20:7. There is never any mention of them ever again being together on the first. The John reference has them together in a closed room after the crucifixion because they were afraid of their fellow Jews. Nothing is said about a worship service or day of rest. And it couldn't have been in recognition of the resurrection because at that time they didn't even believe that the resurrection had taken place.
And the Acts reference might very well have had them getting together to break bread with Paul because he happened to be in town and wanted to talk to them before he had to leave again. The "breaking of bread" can simply be saying that the disciples got together to eat a meal on this particular first day of the week . The phrase, "to break bread", does not have to refer to a religious service - unless it is specifically stated.
But even if the breaking of bread mentioned always did refer to the Lord’s Supper, it had nothing to do with placing a special emphasis on the first (day) because Acts 2:46 says that they broke bread every day.
In neither verse is anything said about worship, or for that matter about honoring the resurrection.
Some say that the end of Mark, (from verse nine to the end), is not original, however, at least verse nine in my estimation appears to be legitimate, (which speaks toward my view that the rest of what is there as likely also original). In Mark 16:9 we read a curious statement not found anywhere else:
Mark 16:9 T/R
9 αναστας δε
πρωι πρωτη σαββατου εφανη πρωτον μαρια τη μαγδαληνη αφ ης εκβεβληκει επτα δαιμονια
There is absolutely no justification anywhere in the scripture to render πρωτη σαββατου as the first [
day] of the
week because the word for the Shabbat here is in a singular form. The excuse for such a rendering everywhere else is that we read σαββατων, the genitive neuter
plural form. However this interpretation, (and it surely is that), completely ignores the fact that everywhere in the LXX-Septuagint version of the Torah, in what is clearly speaking of the weekly day of the Shabbat, the Septuagint renders the word Shabbat in a plural Greek form, and the most common form is σαββατων.
Moreover the most enlightening part of the Mark 16:9 statement is the word prote, (πρωτη), because it is found in the Septuagint version of Lev 23:11, which surely speaks of the Shabbat: for not only is it the word Shabbat in the Hebrew text, in this place, but the Septuagint translators make it known that they understand this in what follows down the passage in Lev 23:15, where the count is commanded to be commenced for the feast of Weeks and Pentecost.
Leviticus 23:11 OG LXX
11 και ανοισει το δραγμα εναντι κυριου δεκτον υμιν τη επαυριον
της πρωτης ανοισει αυτο ο ιερευς
11 And he shall wave the sheaf before the LORD to be accepted of you: the morrow of
the Protes the priest shall wave it
In this text
the Protes replaces the word Shabbat found in the Hebrew text, but as stated above, the following shows that they understood and saw that word Shabbat in the Hebrew text and rendered it as such in verse fifteen, showing that they were not intending to change the meaning of the text but rather to explain it.
Leviticus 3:15 OG LXX
15 και αριθμησετε υμεις απο της επαυριον
των σαββατων απο της ημερας ης αν προσενεγκητε το δραγμα του επιθεματος επτα εβδομαδας ολοκληρους
Leviticus 3:15 Brenton Septuagint
15 And ye shall number to yourselves
from the day after the sabbath, from the day on which ye shall offer the sheaf of the heave-offering, seven full weeks:
This text speaks of the very same day as verse eleven: the morrow of the protes, and the morrow of the Shabbat are the same day in the context, and yet here they render σαββατων instead of πρωτης, surely knowing what they are doing.
However, as usual, the singular form Shabbat from the Hebrew text is rendered in the plural in the LXX, and by the context it is clearly speaking of verse eleven, and the plural form is the most common genitive neuter plural form also found in all places in the N/T where we see in translations the rendering "the first
day of the week", (except for the Mark 16:9 passage quoted above containing the singular form σαββατου).
The translators are straight up wrong for ignoring the most commonly quoted source in the Gospel accounts, and the writings of the Apostles, which is the LXX-Septuagint. The day is divided into two parts and the first portion of the Shabbat, the evening before and night before, is the "first-light" of the Shabbat, the Protos, (protes is just a feminine form). The morrow is the next morning and second portion of the weekly Shabbat.