New Defender's Study Bible Notes
1:10 the Lord’s Day. “The Lord’s Day” most likely refers to the first day of the week, our modern Sunday. Christian congregations evidently had been worshipping on the first day of the week for many years by this time (note Acts 20:7; I Corinthians 16:2), presumably because they had been excluded from any influence in the synagogue worship on the last day of the week.
Furthermore, it would be appropriate to call such a day “the Lord’s Day,” in view of Christ’s victory over death on that day. They thereby were commemorating both Christ’s finished work of creation (Genesis 2:1-3) and His finished work of redemption (John 19:30) by observing their Sabbath day (literally “rest day”) on the day of His resurrection. The grammatical construction does not warrant it to be interpreted as “the day of the Lord” (compare I Thessalonians 5:2; II Peter 3:10). It means “the day belonging to the Lord”; the only similar construction in the New Testament is in I Corinthians 11:20, “the Lord’s supper.” John was first called to address existing situations in the seven churches. He was not being translated to the future “day of the Lord” until the events of the fourth and following chapters. Although there is considerable disagreement on this point among commentators, the evidence favors the “Sunday” interpretation here, even though no other record of this identification has been found in early church documents prior to about A.D. 200. This is merely an argument from silence, however; it even seems reasonable that John’s adoption of the term here set the precedent for its eventual adoption in other churches.