Ephesians 4 says to put off the old man and put on the new man created in God's image in righteousness and holiness. The passage gives several examples. The point is that in order to put off an old character, you must not just stop the wrong, but put on the new and right. To put off dishonesty, put on speaking the truth. To put off stealing, put on working with a generous spirit. To put off slander, put on speaking was is good for edification, to build up. To put off anger, clamor, bitterness, malice, put on kindness, tenderheartedness and forgiveness.
Thus, the principle of substitution applies to how people change. To put off anger and bitterness, substitute compassion. Forgiveness and compassion lead to kindness and love. Refusing to forgive will lead to bitterness and ultimately malice.