~~Alexander Hamilton to John Laurens, August 15, 1782
Do not be conformed to this world, but be transformed by the renewing of your mind [that is, your intellect and will], that you may prove what is that good and acceptable and perfect will of God.
But the things that come out of the mouth come from the heart, and these make a man unclean. For out of the heart come evil thoughts, murder, adultery, sexual immorality, theft, false testimony, slander.
(Notice here that what Jesus just listed the things forbidden in the Ten Commandments. Notice also that He listed "evil thoughts" first. The evil contents of man's heart produce evil desires and evil thoughts in him, and from that starting point comes the commission of the crimes.)
A good man out of the good treasure of his heart brings forth good; and an evil man out of the evil treasure of his heart brings forth evil. For out of the abundance of the heart his mouth speaks.
Conversion is more than a change of opinion. Conversion is a change of heart, for according to the above Scriptures, the heart is the spring of action, and the spring of man's nature. Being a Christian does not mean that we sin, only our sins are forgiven forever. No; being a Christian means being fundamentally changed. Your nature is substituted for God's, and the things we practice in our meditations, words, and actions reveal the extent to which God has changed us.