The main issue with the change of the day from a seventh-day Sabbath to a first-day Sabbath is that the morality of the commandment is not dependent upon the particular day of the week that God calls us to worship Him (God can change the day we worship, if He so chooses-as He has done). The unchangeable morality of the Fourth Commandment is rather firmly fixed upon an appointed time set apart by God for His worship (one day out of seven-"six days shalt thou labour, and do all thy work: but the seventh day is the sabbath of the LORD thy God" Exodus 20:9-10).
For example, in Deuteronomy 5:15 (which pertains to the Fourth Commandment), we would understand these words to relate specifically to the Old Covenant (rather than to the New Covenant):
And remember that thou wast a servant in the land of Egypt, and that the LORD thy God brought thee out thence through a mighty hand and by a stretched out arm: therefore the LORD thy God commanded thee to keep the sabbath day.
Likewise, the words found in Deuteronomy 5:16 (which pertain to the Fifth Commandment) relate specifically to the Old Covenant (rather than to the New Covenant):
that it may go well with thee, IN THE LAND [I.E. THE PROMISE LAND--GLP] WHICH THE LORD THY GOD GIVETH THEE.
These words within the Fifth Commandment are altered and enlarged in the New Covenant by the Holy Spirit to include, "THE EARTH" in Ephesians 6:3, (which in no wise altered the morality of the Fifth Commandment):
That it may be well with thee, and thou mayest live long ON THE EARTH.
In both of these cases (Deuteronomy 5:15 and Deuteronomy 5:16), we find certain parts of God's Ten Commandments that relate to the Old Covenant (and therefore are not part of the morality of the commandments and which would not apply to Gentiles in the New Covenant). Thus, circumstances surrounding the Ten Commandments may change without altering the morality of the commandment itself. This is also true of the Fourth Commandment as it relates to a seventh-day Sabbath that has been changed in the New Covenant to a first-day Sabbath. Such a change does not alter the morality of the Fourth Commandment, because the specific day the Sabbath is observed is circumstantially appointed by God (as a seventh-day Sabbath in the Old Covenant, and as a first-day Sabbath in the New Covenant), rather than being perpetually and unchangeably moral.
We necessarily infer this change to a first-day Sabbath for the following reasons.
1. The day of Christ's resurrection was the first day of the week (the day of the new creation in the mighty creative act of raising Christ from the dead, John 20:1)-why was Christ not raised on the seventh day of the week?
2. Christ's appearance to His apostles as the resurrected Lord was on the first day of the week (John 20:19)-why did Christ not appear to His apostles as the resurrected Lord on the seventh day of the week?
3. Christ's appearance the following week to show himself as the resurrected Lord to Thomas and the other apostles, who were again gather together, was on the first day of the week (John 20:19)-why not on the seventh day of the week?
4. The outpouring of the Holy Spirit occurred on the eighth day or first day of the week (Acts 2:1 compared with Leviticus 23:15)-why not on the seventh day of the week?
5. The worship of the apostolic church was on the first day of the week, as demonstrated by Paul skipping over the seventh day of the week for worship in Troas, and rather gathering with the Christians in Troas on the first day of the week. Paul was present in Troas on the seventh day of the week, but the Church of Troas meets on the first day of the week (Acts 20:5-12)-since Paul was in Troas a full week of seven days, why did he not meet with the Church of Troas on the seventh day for worship?
6. The offerings that were specifically to be given by the Church of Corinth were commanded to be given on the first day of the week (1 Corinthians 16:2)-why not on the seventh day of the week if the Church of Corinth gathered for worship on the seventh day?
7. The use of "the Lord's Day" in Revelation 1:10 points to a first-day Sabbath, rather than to a first-day Sabbath. For the Greek adjective used for "Lord" [kuriakos] in "the Lord's Day" is used only one other place in the New Testament and that is in 1 Corinthians 11:20 to refer to "the Lord's Supper". Just as "the Lord's Supper" is a supper instituted by Jesus Christ to celebrate His death for His people, so "the Lord's Day" is a day instituted by Jesus Christ to celebrate His resurrection for His people.
The only reason for the mention of the seventh-day Sabbath in the Book of Acts (after the resurrection of Christ and the institution of the first-day Sabbath) is because the gospel was to be taken to the Jew first (Acts 13:46; Romans 1:16), and the day and place in which the Jews congregated for worship was on the seventh-day in their synagogues. In other words, in order to reach the Jews, the apostles gathered with the Jews to proclaim to the gospel of Jesus Christ (1 Corinthians 9:20). However, such attendance by the apostles on the seventh-day Sabbath of the Jews at their synagogues was not moral in nature, but expedient and convenient (that is when and where the Jews could be taught the gospel). In fact, the Apostle Paul declares that the seventh-day Sabbath of the Old Covenant (along with the other ceremonial holy days of the Old Covenant) "are a shadow of things to come; but the body is of Christ" (Colossians 2:16-17). The seventh-day Sabbath of the Old Covenant is, therefore, as much a "shadow" of the gospel blessings in Christ, as are the sacrifices of the Old Testament (Hebrews 10:1). The "shadows" of the Old Testament were not moral in nature, and therefore, have been nailed to the cross of Christ (Colossians 2:14) as ceremonies that no longer bind Christians under the New Covenant (Ephesians 2:15). The references in the New Testament to Christ's resurrection on the first day of the week, the Day of Pentecost on the eighth or first day of the week, Christian worship on the first day of the week, and the Lord's Day in celebration of Christ's resurrection on the first day of the week, these together establish (by good and necessary inference and by approved example) the day in which Christ appointed His Church to gather for worship in the age of the New Covenant-the first day of the week!
This is also confirmed by the fact that the Lord's Day was known to be the first day of the week very early in the history of the church.
The following summary clearly demonstrates that it was not Constantine or the Council of Nicea that first changed the Jewish Sabbath (on the seventh day of the week) to the Lord's Day (on the first or eighth day of the week), and that it was not the Roman Catholic Church that was responsible for the alteration from the seventh-day Sabbath to the first-day Sabbath (called the "Lord's Day) within the practice of the Christian Church. It was in fact the practice of the apostles themselves (Acts 20:7; 1 Corinthians 16:2; Revelation 1:10) who followed the example of Christ, who was raised from the dead on the first day of the week (Mark 16:2; Luke 24:1; John 20:1) and who appeared to His disciples on the first day of the week (John 20:19) and again eight days later on the first day of the week (John 20:26). This was likewise the universal practice of early Christians prior to Constantine, the Council of Nicea, or a pronouncement by the Church of Rome.
1. IGNATIUS (30-107 a.d.)
Those who have come to the possession of new hope, no longer observing the Sabbath, but living in the observance of THE LORD'S DAY, on which also our life has sprung up again, by him and by his death (Ignatius, Epistle To The Magnesians, Ch. IX, emphases added).
Ignatius was appointed to be the bishop of Antioch about 69 a.d. This epistle was most likely written 98-107 a.d. He was noted to be a disciple of the Apostle John. Ignatius describes the shift from observing the Jewish Sabbath to observing the Christian Lord's Day.
2. EPISTLE OF BARNABAS (about 100 a.d.)
Wherefore, also, we keep THE EIGHTH DAY with joyfulness, the day also on which Jesus rose again from the dead (Epistle Of Barnabas, Ch. XV, emphases added).
The Epistle of Barnabas (though not canonical), nevertheless sets forth the practice of early Christians in regard to Lord's Day worship or as it is also called worship that occurs on "the eighth day."
3. JUSTIN MARTYR (110-165 a.d.)
ON THE DAY CALLED SUNDAY is an assembly of all who live either in cities or in the rural districts, and the memoirs of the apostles [i.e. the inspired writings of the apostles found in the New Testament--GLP] and the writings of the prophets are read .... BUT SUNDAY IS THE DAY ON WHICH WE ALL HOLD OUR COMMON ASSEMBLY, because it is the first day on which God dispelled the darkness and the original state of things and formed the world, and because Jesus our Savior rose from the dead upon it (Justin Martyr, First Apology Of Justin, Ch. LXVII, emphases added).
Justin refers to the first day of the week in which Christians gather for worship as "Sunday."