The Gospel of the kingdom and the Gospel of the Circumcision are based on covenants GOd made with the Jews. Both were bound up with ordinances and signs. Circumcision was the sign of the Abrahamic COvenant (Gen. 17:11). And water baptism was the sign of the Davidic Covenant (Ex. 29:4, cf. Ex. 19:5,6, Isa. 61:6, Matt. 3:1-6). But WE are gentiles, STRANGERS FROM THE COVENANTS. (Eph. 2:12). We are in the "But NOW" of GOd's plan. If we are strangers from the covenants, are we supposed to keep them? Whether it be circumcision, water baptism, dietary rules, etc. Water baptism can NOT be the One Baptism Paul writes of for us today. "For BY ONE SPIRIT are we all baptized INTO ONE BODY.,.."1 Cor. 12:13. Not physically, Spiritually. Just like we are circumcised by the Holy Spirit. Not physically, Spiritually. THAT is the One Baptism of the dispensation of the grace of God.
Unless a person still desires to be Israel today. WHereby he would be circumsised in fullfillment of the Davidic Covenant and water baptized in fullfullment of the Abrahamic COvenant. Of course, it would do no good, since Israel is now blinded and set aside and God is dealing with individuals, not nations, on an equal basis.
Therein lies part of the problem. The RCC believes Christians have replaced Israel. Many of the organized religions since the split with Rome have followed that line of thinking. I doubt seriously if many of the organized religions of today understand the difference.
"There truly IS ONE BAPTISM in this dispensation. ANd it has nothing to do with water."
"Water baptism can NOT be the One Baptism Paul writes of for us today. "For BY ONE SPIRIT are we all baptized INTO ONE BODY.,.."1 Cor. 12:13. Not physically, Spiritually."
Good stuff. However, I am still curious about your original question. Why was circumcision used? Call me crass, but how does the alteration of certain bodily components (especially THAT component) mean so much? No one should see the alteration, save for a spouse. Why would God give this to Abraham (Gen. 17)? It has always puzzled me.