Great answers so far...
1) The 10th is entirely mental. God not only cares about our actions, He is also concerned with our thought life!
2) It is a "gateway" sin!
Of course all the commandments are to show us we are undone and in desperate need of a savior from God's just wrath.

__________________
Denton Elliott
Husband of one wife, father of three
A striving bondservant of the Lord Jesus Christ
Monroe, GA