The Sabbath (singular) is Jewish, not Greek:
“Remember the Sabbath day, to keep it holy. Six days you shall labor, and do all your work, but the seventh day is a Sabbath to the Lord your God... (Exodus 20:8-10) [ESV throughout]
The ancient Greeks did not have the concept of a week and thus there is no word for 'week' or for any of the days of the week in classical Greek. [The Etymology of "Sabbath"]
- "Sabbath" refers to a singular day which comes at the end not the beginning. It does not refer to the entire 7-day period. It is a singular day of rest following six days of work.
- Using Sabbath to identify the "beginning of the week" is contrary to the meaning of a point in time which comes after working six days.
The plural form of the word should not materially alter the meaning of the singular.
From a practical perspective, any phrase with “Sabbath” or “Sabbaths” is devoid of meaning unless the Sabbath is observed. If the day was “the beginning of the week,” then it is a day known only after the Sabbath was observed. Whether the singular or plural word is used, the Sabbath had to be recognized (by observing the Jewish calendar). Thus, “the beginning of the week” is unlikely since the context is placed with references to the Jewish calendar:
but we sailed away from Philippi after the days of Unleavened Bread… (Acts 20:6)
For Paul had decided to sail past Ephesus, so that he might not have to spend time in Asia, for he was hastening to be at Jerusalem, if possible, on the day of Pentecost. (Acts 20:16)
The implication of recording travels referencing the Jewish calendar through the territories of Macedonia and Asia (where this calendar is not used) is those days were known and observed. If these dates were not observed, what purpose other than to confuse the reader (Theophilus) is served by recording them? More reasonable is to recognize they are included because these times continued to be observed.
This does not directly answer the question about the meaning of "Sabbaths" but a passage which includes “days of Unleavened Bread” and to be “in Jerusalem on the day of Pentecost” presents a challenge for an understanding which implies the Sabbath was not observed. If Paul continued to follow the annual calendar, as the passage suggests, so too he would follow the weekly (as stated elsewhere in Acts). Logically this is the point the passage intends to convey.
There are related questions on this site about the plural Sabbaths: What are the many Sabbaths referred to in scripture? and Colossians 2:16 speaks of holy days, festivals or weekly sabbaths? and Sabbath, Sabbaths or week? Matthew 28:1
The three obvious literal meanings of the plural of Sabbath are:
- More than one weekly Sabbath
- The counting of Sabbaths after the Passover (Leviticus 23:15-16)
- Periods of time with both an annual day of rest and a weekly Sabbath
These are not possible in Troas but it is important to understand Sabbaths as plural is meaningful and could be consistently rendered as such. Both the singular Sabbath and plural Sabbaths are used in the New Testament. However, neither is rendered consistently. Using the King James Version, here is a chart of how the singular and plural of Sabbath are translated:
The plural form is sometimes a week and sometimes a singular Sabbath and it is never called Sabbaths. Also inconsistent is the singular which is rendered as “week” in three places.
Luke uses the plural σαββάτων three times in Acts:
but they went on from Perga and came to Antioch in Pisidia. And on the Sabbath day (ἡμέρᾳ τῶν σαββάτων) they went into the synagogue and sat down. (Acts 13:14)
And on the Sabbath day (ἡμέρᾳ τῶν σαββάτων) we went outside the gate to the riverside, where we supposed there was a place of prayer, and we sat down and spoke to the women who had come together. (Acts 16:13)
On the first day of the week (Ἐν δὲ μια των σαββατων), when we were gathered together to break bread, Paul talked with them, intending to depart on the next day, and he prolonged his speech until midnight. (Acts 20:7)
The first two are always placed on the Sabbath Day. Acts 20:7 is placed after the Sabbath despite describing an event which is taking place during the evening (earlier in the 24-hour Sabbath rest).
Ἐν δὲ μια των σαββατων
The phrase in Acts is nearly identical to the one Luke uses in the Resurrection narrative:
τῇ δὲ μια των σαββατων (Luke 24:1)
Ἐν δὲ μια των σαββατων (Acts 20:7)
The use of the definite article in the Gospel follows the importance of the day: it is the first of the Sabbaths marking the counting to the Feast of Weeks. For Christians it is also the first of the Sabbaths in the New Covenant (as discussed in Gina's answer).
The definite article is not used in Acts since the Feast of Unleavened Bread was past. Instead Luke begins the phrase with ἐν. The preposition ἐν denotes a "fixed position in time place or state." Literally it means what is taking place is "in the first of the Sabbaths” not after the Sabbath(s).
Given the other "Sabbaths" in Acts (13:14 and 16:13) the reasonable assumption is Paul and others observed the Sabbath, which traditionally begins at sunset with a prayer service followed by a meal. If the events are placed on the Sabbath and σαββατων is rendered as singular (as it is everywhere else in Acts), the passage would read:
In the first of the Sabbath, when we were gathered together to break bread, Paul talked with them, intending to depart on the next day, and he prolonged his speech until midnight.
What is described is the typical beginning of the Sabbath; Paul and the others gather after sunset to break bread. Where Acts 13:14 and 16:13 describe events occurring in the synagogue during the daytime, towards the end of the Sabbath, Acts 20:7 describes events occurring in a house during the evening which is the start, or first part of the Sabbath. If σαββατων was treated as it is everywhere else in Acts, the events would be placed at the start ("the first") of the Sabbath.
The “Sabbaths” in Troas
Troas (20:7), Antioch in Psidia (13:14), and Philippi (16:13) demonstrate there is another way to understand the plural “Sabbaths."
Luke describes a Sabbath which begins at sunset, following the Jewish custom. However, they are not in Judea where the entire Jewish community stopped working at sunset. They are in Troas, a Roman colony in Asia. If days were reckoned by Greek or Roman custom, either from midnight or from sunrise, then some in Troas would not conclude their six days of work until after sunset. In this case, the “first” of the Sabbaths comes at sunset on Friday. It is “first” as it is followed by those who start their Sabbath at midnight or sunrise on Saturday.
In any city which the beginning of a day is not reckoned at sunset, there will always be more than one “beginning” to the Sabbath, if there are visitors like Paul or others who choose to begin their Sabbath at sunset (according to Jewish or Biblical tradition) while others must adhere to a civil or legal calendar and continue to work until midnight or sunrise.1
The phrase “μια των σαββατων” describes the practical reality of differing customs in the Gentile world. This is no different than the contemporary situation where some Christians observe the weekly Sabbath beginning on sunset Friday while others in the same city wait until Saturday evening, midnight, or Sunday morning. In this situation the actions of those who start before the others may be described as beginning "on the first of the Sabbaths."
The plural Sabbaths is the correct word to describe the situation because, in practice, when the city is considered as a whole, there are multiple beginnings to the singular (weekly) Sabbath. The plural nature refers to the different times a Sabbath may start. Moreover, an itinerant teacher who sought to deliver the opening prayer on the Sabbath would begin in one household at sunset before going to another at midnight or sunrise.
Finally, most translations add "day" as an implied ellipsis. This is done because the Sabbath is seen strictly as a means to measure time. However, in practice, observing the Sabbath is about rest, being refreshed, gathering for holy convocations and meals. Based on the purpose of the Sabbath the better ellipsis would be “κοινωνία" (fellowship). Then the phrase would be: “On the first κοινωνία (fellowship) of the Sabbaths, when we were gathered together to break bread…”
In this case, Luke omitted the implied "κοινωνία" to avoid confusion with the practice of communion (κοινωνία) with "the breaking of bread." In other words, on the first of the Sabbaths Paul and other gathered for fellowship, which was done with communion and the breaking of bread. The emphasis is on the first of multiple fellowships on the Sabbath.
Sabbaths in Acts
Contrary to traditional interpretation, Luke's use of the plural Sabbaths throughout Acts is purposeful to show an understanding of the challenge a "Jewish Christian" like Paul faced in observing the Sabbath while traveling in the Gentile world:
Notice despite when the Sabbath begins, all share the same period of daylight (ἡμέρᾳ ὁ σαββάτων). What Luke is saying in Acts 20:7 is Paul conducted a "Sabbath service" as was the custom of the Jewish people, except they did not go to the synagogue to pray collectively, they met in the upper chamber of a house (20:8). Also Paul did not go to another house because his teaching continued past midnight nor did not go to the synagogue in the daytime as he did in Antioch of Psidia or to (another) place of prayer as in Philippi.
1. Luke is describing an actual event. He is recording history. He is not commenting on whether the Sabbath should begin at sunset. He is simply stating sunset is when Paul gathered with others for fellowship.