Confession

For people who want a biblical answer:

"Jesus said to them again, 'Peace be with you. As the Father has sent me, so I send you.'

And when he had said this, he breathed on them and said to them, "Receive the holy Spirit.

Whose sins you forgive are forgiven them, and whose sins you retain are retained."

-John 20:21-23

There are other passages too that can help, but this is the most important one to know.