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.
The circumcision that was given to Abraham was an outward sign done on the foreskin of every male to indicate that they were set apart for the LORD. Circumcision of the heart is done by placing the Holy Spirit inside of you, changing you from within. Everyone who claims to be a follower of Jesus has to be different from the world, this is the sign that you belong to Him.
You, however, are not in the realm of the flesh but are in the realm of the Spirit, if indeed the Spirit of God lives in you. And if anyone does not have the Spirit of Christ, they do not belong to Christ.