Why has the Christian church historically called Sunday “the Lord’s Day” or “The Christian Sabbath?” Why do we meet for worship on the first day of the week, and rest on it? William Ames explains this well in his Marrow of Theology (II.XV.27-29):
“Divine not human authority has now changed the last day of the week to the first day – only he can change the day of the Sabbath who is the Lord of the sabbath, namely, Christ (Mt. 12:8). Therefore, the first day… is properly called the Lord’s Day. Even though the Lord’s Day is granted to have been of apostolic institution, yet the authority on which it rests is nonetheless divine, for the apostles were guided by the Spirit in holy practices just as they were in propounding the doctrine of the gospel by word of mouth and writing.”
Ames goes on to give nine points to defend the divine institution of the Lord’s Day as the first day of the week. I’ll summarize the nine points here:
1) Christ was no less faithful than Moses in ordering his whole house (the church of God) in all things generally necessary and useful (Heb. 3:2, 6). No Christian can reasonably deny that the observance of the day is useful and in some way necessary for the churches of Christ.
2) Christ himself often appeared upon this very day to the disciples gathered in one place after the resurrection (Jn. 20:19, 26).
3) The Holy Spirit came upon them this very day (Acts 2:4).
4) In the practice of the churches in the apostles’ time when mention is made of the observance of the first day (Acts 20:7, 1 Cor. 16:2), it isn’t remembered as a recent ordinance but as something long accepted by the disciples of Christ.
5) All things the apostles delivered to the churches were from Christ (1 Cor. 11:23).
6) The placing of the holy sabbath of the Jews on the seventh day was abrogated by the death of Christ.
7) It does not make sense to say that there were several years between Christ’s death and the observance of the first day, because it would be like saying there were only nine commandments during this time.
8) The reason for the change by the consent of all is the resurrection of Christ which itself is a confirmation. On this day the creation of anew world, or world to come (Heb 2:5), wherein all things are made new (2 Cor. 5:17) are completed, and God in Christ’s rising from the dead ceased and rested from his greatest work. Just as it was in the beginning, so it is also right that the very day wherein Christ rested from his labors should be hallowed (cf Ps. 118:24 and Mt. 21:42).
9) It was also most appropriate that the day of worship in the NT should be ordained by him who ordained the worship itself and from whom all blessing and grace is to be expected in worship.
These are some helpful points! Sometimes we may doubt the “first day sabbath” principle because there isn’t one or two clear texts that teach it. However, when considering the Bible’s bigger picture and the flow of redemptive history centered around Christ, it does make biblical sense to call the first day of the week the Lord’s Day, the day of rest and worship. After all, the people of God received a new calendar after God rescued them from Egypt (Ex. 12), so it surely makes sense that his people would get a new calendar after the New Exodus: rescue from sin and hell!