Romans 2:29

But he is a Jew who is one inwardly; and (true) circumcision is circumcision of the heart, by the Spirit, not by (the fulfillment of) the letter (of the Law). His praise is not from men, but from God.  

Faith and following the leadership of God in our lives is a heart thing. Being born again switches the heart’s focus from darkness to light. Following God without a change of heart would be a constant battle because our minds would not be renewed. Being a Christian starts with developing our Spirit (heart) and willingly following the guide of the Holy Spirit.