The most difficult command of all

Romans 12:14
Bless those who persecute you;
  bless and do not curse

  . 

A new heart

Ezekiel 36:26

I will give you a new heart
and put a new spirit in you;
I will remove from you your heart of stone
  and give you a heart of flesh.

Hebrews 4:12

For the word of God is living and active.
Sharper than any double-edged sword,
it penetrates even to dividing the soul and spirit,
joints and marrow:
it judges the thoughts and attitudes of the heart.