What is the worst sin out there?  If you believe a lot of popular pastors it's homosexuality, abortion or maybe pornography.  While there is no denying the destruction these things bring, they're not the worst.  Is it pride?  Is it greed?  No, but getting closer even our churches tend to struggle with being materialistic and greedy.  Before, I give my answer I want to make one thing clear.  The penalty of sin is the same regardless of the sin.  Our God is a holy God and our sin(big or small) separates us from God.  Our sin is our rebellion against a Holy God.  Christians have been given a covering for their sin.  They exchanged their crappy life for God's perfect life and He got the death we all deserved.  With that being said, I believe the the worst sin we have is the sin that we don't repent of.  Luther said the Christian life is a life of repenting.  How dare we know to do good and don't do it.  How can we see something is clearly wrong in scripture and continue in it?  I wish I hated sin as much as God does.  Someone once said we only believe the parts of the bible we actually follow. 

But God's firm foundation stands, bearing this seal:  "The Lord knows those who are his,"  and ,  "Let everyone who names the name of the Lord depart from iniquity."  2 Timothy 2:19