Two things: the dying-away of the old self, and the coming-to-life of the new. (see Heidelberg Catechism Q&A 88)
- What do you mean “dying-away of the old self”? – It is to be genuinely sorry for sin, to hate it more and more, and to run away from it.
- What is the coming-to-life of the new self? – It is wholehearted joy in God through Christ and a delight to do every kind of good as God wants us to.