"Bitterness is an acid that destroys its own container."
The heart of sinful man is hate, anger, revenge, jealousy, and to get even with those who offend us.
The heart of Jesus from the cross:
Then Jesus said, “Father, forgive them, for they do not know what they do.” (Luke 23:34 NKJV)
Ephesians 4:31-32New King James Version (NKJV)
31 Let all bitterness, wrath, anger, clamor, and evil speaking be put away from you, with all malice. 32 And be kind to one another, tenderhearted, forgiving one another, even as God in Christ forgave you.
Love Your Enemies
43 “You have heard that it was said, ‘You shall love your neighborand hate your enemy.’44 But I say to you, love your enemies, bless those who curse you, do good to those who hate you, and pray for those who spitefully use you and persecute you,45 that you may be sons of your Father in heaven; for He makes His sun rise on the evil and on the good, and sends rain on the just and on the unjust.46 For if you love those who love you, what reward have you? Do not even the tax collectors do the same?47 And if you greet your brethren only, what do you do more than others? Do not even the tax collectors[j] do so?48 Therefore you shall be perfect, just as your Father in heaven is perfect.