Circumcision seems to me to be a weird choice for the mark of God’s people, but God never undertakes to explain why he chose it. To Abraham God had said: “Every male among you shall be circumcised. You are to undergo circumcision, and it will be the sign of the covenant between me and you. For the generations to come every male among you who is eight days old must be circumcised, including those born in your household or bought with money from a foreigner—those who are not your offspring. Whether born in your household or bought with your money, they must be circumcised. My covenant in your flesh is to be an everlasting covenant. Any uncircumcised male, who has not been circumcised in the flesh, will be cut off from his people; he has broken my covenant” (Genesis 17:11ff).
Was He serious?
As the story of Moses begins, there is a circumcision story. Moses had failed to circumcise his sons, and God set about to kill Moses until Zipporah (Moses’ wife) performed the circumcision to save him.
As the story of Joshua begins, we have this circumcision story. Before the people of promise can enter the land of promise, they must have the mark of the people of God.
It would appear God was serious.
Every covenant of God had its marks. With Noah it was a rainbow. With Abraham it was circumcision. With Israel it was the Sabbath (Ezekiel 20:12). With Christians it is the presence of the Holy Spirit, which is seen in our lives as we follow His leading into love, joy, peace, patience, kindness, goodness, faithfulness, gentleness and self-control (Galatians 5:22).
Is God serious about the sign being there?
He always has been before.