Deuteronomy 30:6
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.
This comes a few verses after yesterday's, so it comes after the prophecy that God would bring Israel back to Israel, more numerous and prosperous than before. Moreover, God would circumcise their hearts, with the result that they can better love him with all their hearts.
I once heard a good radio preacher speak on circumcision, and I wish I could remember all he said. He analyzed circumcision as a ritual with spiritual meaning. I remember he said circumcision affected the root of creativity, or something to that effect.
Circumcision, I've witnessed a few of them, from my days assisting Dr. Dotson to sitting with baby Christian. In the olden days I believe it was done more in a religious setting, with a flint knife. The baby lies restrained, his most delicate external areas exposed, and a bit of skin is cut off. Interesting, the skin might be argued to have some function, and it can usually stay on without hurting anything, but it can be cut off. Not without hurting. It does hurt. Dr. Blair used novocaine, too humane to "do surgery without anesthetic," but that hurts in itself. The experience is frightening, if not terrifying. But it heals. Some say the private member is then more hygienic, less likely to spread certain diseases to the mate, even "more handsome." It is unmistakable in appearance, at any rate.
How does that apply to circumcision of the heart? If it were similar, you could say it hurts, and is upsetting, and it takes off something, like pruning the vine, something that might seem natural and even good.
You would have to say the heart--the innermost self, the core--is better off. It looks different, it has God's trademark on it. It is cleaner, less likely to harbor evil.
And it is enabled to love God wholly as it never could before.