We have to remember that God is just as much concerned about sin now as He was when He inspired the prophets of old; concerned with the sins of those He would call His own. 'Love God' is the command Christ gave first priority out of all God's commands. If we obey this command and do love God who first loved us we will want to be done with sin - first our own then, once we are children of God, praying for others like us to be freed from their sins too.
