Peter used the Law of God in his first sermon to point out to the crowd their sin of murder and rebellion against God. Here is how it is recorded in Acts, “Now when they heard this they were stung (cut) to the heart, and they said to Peter and the rest of the apostles (special messengers), Brethren, what shall we do? And Peter answered them, Repent (change your views and purpose to accept the will of God in your inner selves instead of rejecting it) and be baptized, every one of you, in the name of Jesus Christ for the forgiveness of and release from your sins; and you shall receive the gift of the Holy Spirit. [Acts 2:37-38 AMP]
When a person has a diseased physical heart, death is certain unless they can somehow receive a gift of someone else’s heart. This is the same exact problem with humanity! There is no way to reform a person, they will never change. Therefore, God must do a miracle and give a new heart and spirit to cure them of their sick spirit. “I’ll give you a new heart, put a new spirit in you. I’ll remove the stone heart from your body and replace it with a heart that’s God-willed, not self-willed. I’ll put my Spirit in you and make it possible for you to do what I tell you and live by my commands.” [Ezek 36:26-27 THE MESSAGE]
Matt 4:17 AMP
From that time Jesus began to preach, crying out, Repent ( change your mind for the better, heartily amend your ways, with abhorrence of your past sins), for the kingdom of heaven is at hand.
In this talk Randy explains the true depth of the repentance God accepts.