"...He [Satan] was a murderer from the beginning, and does not stand in the truth, because there is no truth in him."

John 8:44

When you sin, you are essentially allying yourself with Satan. 

He delights when we submit to the temptation of breaking God's laws.

We put his agenda ahead of God's. 

You would invite a murderer into your own home?

"...He was a murderer from the beginning..."