In a similar vein related to the first day of the week, which I associate with the eighth day:
The number “8” has to do with the new creation, and so does the number “50”….which is (7 X 7) + 1.
Jesus worked 6 days (symbolically) in his ministry, and finished his work on the cross on Friday (“It is finished”) then rested in the grave on Saturday. He was resurrected on Sunday (day 8) as a new creation (in terms of his resurrection body; not in terms of being YHVH).
Jesus is the BEGINNING of the new creation; the firstfruits (I Corinthians 15, Revelation 3:1).
Hebrew children were physically circumcised on the 8th day, which is a physical type of the new birth or the new creation or being born again (Leviticus 12:3).
On the first Pentecost after the Exodus (which is calculated as the 50th day from the weekly Sabbath during Passover), the Israelites received the Law on Mount Sinai (by Jewish tradition), and became a new physical nation that typified the Church.
On the first Pentecost after the resurrection of Jesus, the Holy Spirit was received by the apostolic church, and the Church became a new spiritual nation; a kingdom of priests (Acts 2).
On the land sabbath year, at the end of the year, all debt was forgiven, and there is a new beginning starting in the eighth year (Deuteronomy 15:1-6). This is symbolic of Jesus and the forgiveness of our sins to begin a new life.
On the Jubilee year, which is the 50th year in the Israelite calendar system, all debts were forgiven and the land was returned back to the original property owners; in essence a new life and a restoration (Leviticus 25:8-15). For the believer, this relates to the liberation that we receive in Jesus, where our spiritual debt is forgiven.
So, these things point toward the new creation, which starts with Jesus’ resurrection. For us, regeneration (being born again) is the beginning of our new life. Ultimately, the new creation reaches fulfillment in a New Heavens and New Earth/New Jerusalem (Revelation 21-22).
The believer has already entered into the new creation, by being united through faith with Jesus. Due to this union, his resurrection, which is our resurrection too, makes us into a new creation. The new creation will be fully consummated upon Jesus' return, but believers are experiencing it, even now. See 2 Cor 5:17, Romans 6:1-14, Hebrews 6:4-6 in relation to this. Romans 4:25 indicates that believers are vindicated along with Christ in his resurrection, and this identifies believers with his resurrection. When he was resurrected, the believer was resurrected too.
I believe this is the theological justification for the day of worship being on Sunday rather than the Jewish Sabbath. And, I believe that Judaizers are trying to live under the old, Mosaic economy rather than stepping into the new creation in Christ.