Dealing with the "Fakers"

I am actually caught up enough on my other book Bible studies that I got to get back to just reading 1 Corinthians today.  My other two studies have been great and are showing me a lot of great stuff, but it is nice just to read the Bible on my own and think and pray without having to wonder if I will come up with the same 'answer' as the author or other people doing my studies.

Today I read 1 Cor 5:9-13.  Here Paul talks to the Corinthians about separating themselves from immoral people.  Not immoral non-believers, but immoral people who claim to be Christians.  "With such a man do not even eat." v. 11

Pretty powerful stuff.  It confuses me a bit.  Paul says it is OK to be around non-Christians who are doing immoral things, because God will be their judgement.  He also says if we cast ourselves away from these people there wouldn't be anyone left in the world to be around.  I can only assume that separating ourselves from worldly people would be quite detrimental in the ways of Evangelism as well.  Otherwise we would only be "preaching to the choir."

My question comes on how to define an "immoral Christian".  I guess it is my understanding or belief that if you truly accept Christ as your Lord and Savior your life cannot help but to be changed.  So, if you keep on living life as you did before Christ, are you really a believer at all?  How are we to separate the two?

My assumption would be that Paul is not actually calling these men believers, but telling the true Corinthian believers not to associate with worldly believers who are falsifying their Christianity.  My questioning comes in when I start wondering how we are to truly convert the 'fakers' to believers if we detach ourselves from them?

The things that make me go, "Hmmm?" 

The last two verses I read give a little clarity to my question, but also leave me with even more questions.  (Oh, the complexity that is me, sorry to involve you in it.)  They state that God is in charge of judgement of those outside of the church, but "Are you not to judge those inside?  ...Expel the wicked man from among you." v. 12b & 13b 

Going on what I assume the Holy Spirit to be leading me to understand is that our "judging" is more like discipline and direction of those claiming to be part of the body of Christ because God makes it clear in His Word that He is indeed in charge of true judgement that really counts. 

I did a search on the words "judge not" on biblegateway.com and, through a quick scan, did not find a verse that says we are not to judge our fellow believers, but that we are to do so in the correct way.  Again, leading me to believe that this judgement is discipline and direction that we are all subject to as part of Christ's church or even if we just claim to be a part of it.

Man, how I love how things evolve as I keep typing.  Thank you, Holy Spirit!