28 A person is not a Jew who is one only outwardly, nor is circumcision merely outward and physical. 29 No, a person is a Jew who is one inwardly; and circumcision is circumcision of the heart, by the Spirit, not by the written code. Such a person’s praise is not from other people, but from God.
Verses that refer to circumcision of the heart are found throughout the Old Testament and they refer to a condition of the heart although not always directly mentioning circumcision.
Circumcise your hearts, therefore, and do not be stiff-necked any longer.
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.
Circumcise yourselves to the LORD, circumcise your hearts, you people of Judah and inhabitants of Jerusalem, or my wrath will flare up and burn like fire because of the evil you have done– burn with no one to quench it.
My sacrifice, O God, is a broken spirit; a broken and contrite heart you, God, will not despise.
But the LORD said to Samuel, “Do not consider his appearance or his height, for I have rejected him. The LORD does not look at the things people look at. People look at the outward appearance, but the LORD looks at the heart.”
1 Samuel 16:7
So what do we mean when we say circumcision of the heart? Barnes Notes on the Bible gives a good explanation
And circumcision is that of the heart – That is, that circumcision which is acceptable to God. and which meets the design of the institution, is what is attended with holiness of heart; with the cutting off of sins; and with a pure life. The design of circumcision was to be a sign of separation from the pagan world, and of consecration to the holy God. And this design implied the renunciation and forsaking of all sins; or the cutting off of everything that was offensive to God. This was a work especially of the heart.
Clearly this is a tough order for Jew and Gentile alike or Jew and Christian alike. Still the key here is to seek the approval or praise, not from other people, but from God. God’s praise is only given to those who truly seek His will and do their best to align their lives with His will – internally and not to empty ritual requirements.
While the verses are stated for professing Jews, they are just as applicable to professing Christians. After all, the rituals of our Christian religion are of little value when compared to the importance of the condition (circumcised) of the heart. What others observe in our behavior does not determine our true character as far as God is concerned – the condition of our heart does. That is a certainty we should contemplate with an awareness that God knows what is in our hearts.
Forgive and act; deal with everyone according to all they do, since You know their hearts (for You alone know every human heart), so that they will fear You all the time they live in the land You gave our ancestors.
1 Kings 8:39b-40
So what are we to do? Seek His approval, not the approval of others. The approval of others is nice to have, but the key to our eternal future is to seek His approval, not theirs. How do we do that, seek His approval? By study of His word, prayer, and putting His word into action in our individual lives. We know from yesterday’s verse of the day, the requirements of the law are written on their hearts. We would do well to remember this as we go through with what each day presents us.