As a Christian, I need to train my heart, because:
The world has a lot of influence! It wants us to be squeezed into its mold.
We still deal with the remains of sin. Standard behaviors, stock responses – we need to learn new habitual reactions.
A well-trained heart glorifies God – and that's ultimately what we want to do.
"Dear God, please give me a love for those unlovely – help me see people not through these earthly eyes, but through Christ's. ~Amen"