Why does Paul put the spotlight on regeneration in Galatians 6:15?  It’s because of how it sharply contrasts with circumcision: 1. Regeneration is an inward work of the heart that no one can see, although the results of it can be seen; 2. It’s a sovereign work of God which man has absolutely no part in.  The only thing man contributes to regeneration is his status as a sinful human.  Just like none of my daughters will never say, “I’m so glad I decided to be born,” nobody wakes up in the morning and says, “I think I’m going to regenerate my heart today.”

Jesus is crystal clear in John 3—the spirit blows where he wishes or in other words transforms whom he wills and He says unless someone is born again he cannot enter heaven.  Think about this—If being a new creature is a sovereign act of God and that’s the only thing that matters, then God gets all the glory because there’s absolutely no way man can take credit for that.  Now you can see why Paul boasts in the cross.  The cross gave him life.  Before the cross he was dead, thinking he could make a good showing in the flesh before a holy God, but now he’s alive, he’s a new creation.  The old things are gone.  Being born again and set free from worshipping himself was everything to Paul.  That’s why the focal point of boasting can never be on man, but on the cross of Christ which secured this gracious gift of being transformed into a new creation.