Do I not hate those who hate you, O Lord?
And do I not loathe those who rise up against you?
I hate them with complete hatred;
I count them my enemies.
This was a difficult passage to write a commentary for, but here it goes:
In the New Testament Jesus tells us in Matthew 5:43-44, "You have heard that it was said, 'You shall love your neighbor and hate your enemy.' But I say to you, Love your enemies and pray for those who persecute you," Jesus has given us additional teaching on the treatment of our enemies.
One additional thought (a possibility): When David is referring to hating those who hate the Lord, he is referring to how he feels abou them, whereas Jesus is referring to treatment of those enemies.