Nothing in the New Testament leads us to observe the Sabbath. What we see beginning in the gospels and continuing in the rest of the New Testament is a break from the Sabbath with a new emphasis on the first day of the week.
Each gospel writer carefully points out that Jesus’ resurrection was on the first of the week, Matthew 28:1, Mark 16:1-2, Luke 24:1 & John 20:1. Why did the Holy Spirit inspire each of these men to record this fact unless to make a point with the reader?
Jesus began his church on the feast of Pentecost, which fell on the 1st of the 8th week. “Pentecost” is the Greek name given to the original feast of the harvest (the feast of weeks) because it fell on the 50th day after the Passover (Exodus 23:16, 34:22, Leviticus 23:15-16, Numbers 28:26 & Deuteronomy 16:6-11).
You ate the Passover lamb whose blood spared God’s people from death at the designated time for the Passover feast. Then you counted seven Sabbaths (49 days) and on the next day, the 50th day, the 1st day of a new week, you celebrated the harvest.
The harvest feast of Pentecost seemed specifically designed to lead Israel to this 1st day of the week. God raised his slain lamb (our Passover) on the 1st day of the week and then ordained the 1st day of the week by sending his Holy Spirit to the apostles on the 1st Pentecost following Jesus’ resurrection. On this day, Jesus church was established (Acts 2).
The first day of the week is also the day that God reports to us that the saints assembled to break bread (Acts 20:7) and the day upon which the saints were to make their own sacrifice for the saints (1st Corinthians 16:1-2). Rather than being random or incidental matters, these points of scripture appear more like guideposts leading us in the direction God desires.
Are there New Testament references to any other day of the week, the 2nd, 3rd, 4th, etc.? Not that I know of. Only the first is noted, and this from the gospels on.
As J.W. McGarvey once said, “Those who are willing to be guided by the slightest indications of the will of God in preference to their own judgment, will find sufficient to satisfy them”.