Chapter 14 is one of the shortest sections in the entire Didache, comprising only three verses. It continues in the broader section of legal rulings (chapters 11-15).
The contents of this chapter are concerned with resolving community sins and quarrels and maintaining the purity and unity of the congregation.
The Lord’s Day
On the day of the Lord, being gathered together. (Didache 14.1)
Chapter 14 opens up with one of the most controversial phrases in the entire Didache. Without any introduction or explanation, the Didache states that the community will be gathered together on “the day of the Lord.”This is not presented in command form but rather assumes that the audience knows exactly what this term means and is well aware of the practice. The Apostolic Constitutions renders this in command form: “Gather together, without fail” (7.30).
Although the opening words of chapter 14 are usually translated into English as “the day of the Lord” or “the Lord’s day,” the Greek is more ambiguous. Kuriaken de kuriou is a redundant phrase that can be translated literally as “Lord’s of the Lord,” which is something to the effect of “Lord’s day of the Lord” or “the Lord’s own day.” Some scholars have suggested that this is a Semitism based upon the Torah’s phrase “Sabbath of the LORD,” where the Didache replaces “Sabbath” with “Lord’s” to mimic the Hebrew designation.
Saturday or Sunday?
Many commentators are quick to see this as an early reference to Christian veneration of the first day of the week. This is how it is rendered in the Apostolic Constitutions: “On the day of the resurrection of the Lord, that is, the Lord’s day” (7.30). The evidence may not be that clear-cut. The appearance of “the day of the Lord” in the Didache is the first witness of the title. The phrase “the Lord’s day” (tekuriake hemera) does appear one time in the New Testament in the book of Revelation, but no designation is given as to which day it refers. “It is not until the second century CE that unequivocal references to weekly Sunday worship can be found” and the phrase “the Lord’s Day” is directly connected to the first day of the week.  Furthermore, in the New Testament, Sunday is always referred to as “the first day of the week.”
Aaron Milavec feels that the Greek could be translated as “every divinely instituted day of the Lord” or “divinely instituted day.”  He adds, “Given that the Jewish calendar dominates the Didache, the ‘divinely instituted day’ could refer either to the Sabbath or the first day of the week.”  It’s possible then that “the Lord’s day” “might have been an uncommon, apostolic way of referring to the Sabbath day, as Yeshua said, ‘For the Son of Man is Lord of the Sabbath’ (Matthew 12:8). This explanation is attractive for Sabbatarians, and it might find corroboration in the Acts of John at Rome: ‘on the seventh day, the Lord’s day.’” 
A few other suggestions have been proposed as well. Some who hold that the expression “the Lord’s day” refers to Sunday view the double repetition in the Didache “the Lord’s day of the Lord” as an emphasis that this is not just any Sunday but specifically Resurrection Sunday (Easter Sunday). Neville Tidwell feels that the phrase is a reference to Yom Kippur. The language of “Lord’s of the Lord” is similar to the Torah’s description of Yom Kippur as the Sabbath of Sabbaths (Shabbat Shabbaton), both phrases emphasizing the day of which they are speaking as “the most solemn of days.”  Yom Kippur is about atoning for sins against God and making things right with one’s fellow, which parallels the instructions of Didache 14. This opinion, however, is difficult to reconcile with the biblical prohibition to eat or drink on that day.
Samuele Bacchiocchi, citing Jean Baptiste Thibaut, states that “‘Lord’s—kuriaken’ is used as an adjective and not as a substantive and that the issue is not the time but the manner of the celebration.”  Furthermore, based on its close proximity to the end of chapter 13, “according to the commandment,” he insists that the opening word kata should be translated as “according to” as it is in 1.5, 2.1, 4.13, 6.1, 11, and 13.6, resulting in “according to the sovereign doctrine of the Lord.” 
The most probable answer is that “the day of the Lord” refers to a ceremonial community meal that took place on Saturday night after the Sabbath concluded. Varner writes:
It follows that the meal was taken in the evening, since that would be when a meal is taken and [since] work obligations would have prevented something as important as this in the daytime … I am not convinced that Sunday evening was the practice of the Didache believers, since in Jewish custom, evening marks the beginning of the next day. 
We see the custom of gathering on Saturday evening in Acts 20:7. “On the first day” and “after the Sabbath” is the time of the Master’s resurrection, that is, Saturday night. The early believers seem to have gathered after the Sabbath to commemorate the resurrection and to share a special meal. While the believers may have attended their local synagogues on Shabbat, they could then have gathered together in the evening without the encumbrances of the Sabbath’s prohibitions.
The custom of holding a meal on Saturday night after the Sabbath, called Melaveh Malkah, is still kept today in many Jewish circles. As Christianity separated from Judaism and lost its Jewish associations, Sunday became associated with the Lord’s Day, but originally the disciples would have gathered on Saturday night.
In addition to meeting at the conclusion of the Sabbath in memory of the resurrection of the Master, it is possible that the community expected his return at this time. Jewish tradition states that Messiah will not come on the Sabbath because there is much work to do upon his arrival. Therefore, the first possible time for his appearance would be at Melaveh Malkah. Appropriately, this meal is also known as Seudata d’David Malka Meshicha (The Meal of David, King Messiah). Furthermore, upon the return of Messiah, there will be a great banquet.
- Jonathan A. Draper, “Pure Sacrifice in Didache 14 as Jewish Christian Exegesis,” Neotestamentica 42, no. 2 (2008): 223-252. E.g., Ignatius, To the Magnesians 9; Barnabas 15.9; Gospel of Peter 1.9, 12; Apostolic Constitutions 7.30, 36. Justin Martyr mentions holding a “common assembly” (First Apology 67) on Sunday, and Tertullian was the first to mention resting on Sunday, “on which day it is our duty to free ourselves from all worldly care and trouble, even postponing business, lest we should give place to the devil” (George Cantrell Allen, The Didache or the Teaching of the Twelve Apostles [London, England: Astolat, 1903], 23).
- Aaron Milavec, The Didache: Faith, Hope, & Life of the Earliest Christian Communities, 50‒70 C.E. (New York, NY: Newman, 2003), 533-534.
- Ibid., 573.
- D. Thomas Lancaster, Torah Club: Chronicles of the Apostles (Marshfield, MO: First Fruits of Zion 2012), 1215.
- Neville Tidwell, “Didache XIV:1 (Kata Kuriaken de Kuriou) revisited,” Vigiliae Christianae 53, no. 2 (1999): 197-207.
- Samuele Bacchiocchi, From Sabbath to Sunday: A Historical Investigation of the Rise of Sunday Observance in Early Christianity (Rome, Italy: Pontifical Gregorian University, 1977), 125-126.
- Daniel Stokl Ben Ezra, The Impact of Yom Kippur on Early Christianity: The Day of Atonement from Second Temple Judaism to the Fifth Century (Tubingen, Germany: Mohr Siebeck, 2003), 217.
- William Varner, The Way of the Didache: The First Christian Handbook (New York, NY: University Press of America, 2007), 78.