Being circumcised was a sign God gave to prove Abraham and his descendants were set apart. Later on, when Moses led those descendants out of Egypt, God gave them another sign to prove they were not only descendants of Abraham, but they were God’s chosen nation and would follow his laws. Circumcision and keeping the Sabbath were the two most obvious observances kept by the Jews that made them different from those around them. The Jews and those converting to Judaism believed they needed to keep both to prove they belonged to God. Both signs were equally binding.
Genesis 17:9-11 New Century Version
9 Then God said to Abraham, “You and your descendants must keep this agreement from now on. 10 This is my agreement with you and all your descendants, which you must obey: Every male among you must be circumcised. 11 Cut away your foreskin to show that you are prepared to follow the agreement between me and you.
Exodus 31:12-15 Contemporary English Version
12-13 Moses told the Israelites that the Lord had said: The Sabbath belongs to me. Now I command you and your descendants to always obey the laws of the Sabbath. By doing this, you will know that I have chosen you as my own. 14-15 Keep the Sabbath holy. You have six days to do your work, but the Sabbath is mine, and it must remain a day of rest. If you work on the Sabbath, you will no longer be part of my people, and you will be put to death.
For new Christians coming out of Judaism, keeping the rules and laws unassociated with the sacrificial laws was an assumption a lot of them made. The Jews argued for circumcising Gentiles because they thought any male wanting to join the family of God, had to become a Jew and be circumcised. The fact the New Testament records no controversies over not keeping the Sabbath, supports the belief the Christian day of worship was never biblically changed from Saturday to Sunday. Had the apostles changed the day, controversies like that surrounding circumcision would have surely ensued.
The New Testament has several often missed references to God’s annual holy days. Had the early Christians not been keeping those annual days then why use them as a reference. What do you know about God’s annual holy days?
Acts 27:9 King James Version
9 Now when much time was spent, and when sailing was now dangerous, because the fast was now already past, Paul admonished them,