We are heirs according to promise, but under the law until we come of age. Now that Christ and the Spirit have come we are no longer under the law. Why go back to it? You are leaving the Gospel I (Paul) preached, no longer esteeming me as you once did.
The Ishmael and Isaac history is repeating itself: Jews apart from Christ are Ishmael, physically of Abraham but not receiving the promise. Christians are Isaac, children of the promise.
If you go back to following the law as your identity and trust, then you have left Christ, fallen from grace. In Him, only faith working through love matters, not the law. I (Paul) am not preaching circumcision to you. I wish those who are would go further and cut more off. The law of freedom is to love and serve each other. The fruit of the flesh and of the Spirit are each obvious and opposed to each other.
Restore sinners gently, not sinning yourself. Sow a harvest for yourself and beyond, to share with others in need.
Circumcision advocates are counting noses for Moses. Look how great Moses is, how many followers he has! I boast only in the cross of Jesus Christ. There you find the real circumcision. Believers in it are the real Israel of God. Don't give me any more grief about this; I have scars elsewhere on my body because of Jesus.
APPLICATION: what belief or practice that is important to you comes closest to defining your identity, your faith, supplanting Christ and His cross?
Live and let live
Your family being together
The commandment to be Nice, and not offend
Gender roles in marriage and family