Galatians 5:2 Look: I, Paul, say to you that if you accept circumcision, Christ will be of no advantage to you. 3 I testify again to every man who accepts circumcision that he is obligated to keep the whole law. 4 You are severed from Christ, you who would be justified by the law; you have fallen away from grace. 5 For through the Spirit, by faith, we ourselves eagerly wait for the hope of righteousness. 6 For in Christ Jesus neither circumcision nor uncircumcision counts for anything, but only faith working through love.
This does not negate Abraham's faith which led him to obey God and be circumcised. THAT was the first (Old) covenant.
Note the 'in Christ' part of your reference, which says that neither circumcision nor uncircumcision is the basis for New Covenant faith.
The NEW covenant (testament) is based, not on circumcision, but on Jesus' sacrifice...circumcision of the heart.
Paul's point was to show those who trust in the works of the law are obligated to keep all things in the law.
6 The Lord your God will circumcise your hearts and the hearts of your descendants, so that you may love him with all your heart and with all your soul, and LIVE.
7 The Lord your God will put all these curses on your enemies who hate and persecute you.
The Law could NOT save anyone...
We have been redeemed....
2 Corinthians 5:21
21 God made him who had no sin to be sin for us, so that in him we might become the righteousness of God.