well, the thing is, on one hand you have sin, and on the other hand you have the spirit.
these two thing are in conflict with each other.
but rewards of the spirit and great, and the reward of sin is death.
also, the thing that gets me every time when i read Galatians 5 is that when we live by the spirit, we are not under law.
look read
http://www.biblegateway.com/passage/?search=Galatians+5&version=NIV