One thing which is true, and of which every discerning Christian should be aware, is that when one’s theology has a serious error, this will almost always lead to a compiling of errors. It is rare when one has a major error in one part of his theology with no further problems.
Let me give an example:
Look at every denomination which has allowed women pastors (UCC, UMC, PCUSA, Episcopal Church, ELCA) and you will see how they soon approved of homosexuality, abortion, and the social gospel.
What happens when churches leave behind the plain reading of Genesis 1 and bend it to fit evolution? Noah’s flood also disappears. Other texts become fables and analogies.
Look at the cults and how one change leads to others until they are full-blown heretics.
What about individuals? I have found the same thing. Let me give an example of what happened to a very dear friend of mine who became a Christian in his early 20s.
This friend has a brother who also became a Christian many years later, but with a more legalistic fellowship which considers worshiping on the Sabbath to be required for Christians. This brother has decided what is and what is not to be considered holy in regards to other issues. For example, if one mentions a that a young lady is growing into a beautiful woman, or that she is pretty, then it must be because the person saying such is lusting after the young lady. Apparently you can only speak of a woman in such a manner if she is your wife or blood relative. In other issues this brother claims that, although my friend did not claim to believe something, the brother said that didn’t matter because he, the brother, knew what my friend was really thinking.
Now that you have an idea of how legalistic theology has led to being un-biblically judgmental, let me tell what recently happened. My friend’s brother brought up all sorts of sins from my friend’s past - from the time he was a young teen until he became a Christian - and railed about what a horrible person my friend was then, and how he is really the same person as he was then. I know my friend very well, and have known him for years, and he has often talked about how he is glad to have been saved from the sinful life he led before Christ forgave him. He is certainly not the person his brother claims he is.
You see, legalistic theology has blinded my friend’s brother to the forgiveness in Christ, and that in Christ we are all new creatures. His brother is still holding grudges from things that happened to him 45 years ago, and cannot understand that he himself was a sinner who Christ forgave!
I have seen this behavior over and over again in many legalistic assemblies and by many legalistic Christians. They are extremely judgmental, claiming to know what is in the hearts of fellow believers, and pointing out every sin they know about, and forgetting that they are also sinners saved by grace. Forgiveness is one of the main things I have found lacking in all these situations.
The moral of my story? Remember that you, too, are a sinner. God has forgiven you through Christ and holds no grudges for past sins, let alone current ones. Therefore, just as God through Christ has forgiven you, you also are to forgive your brothers and sisters in Christ and let go of grudges from sinful pasts. Don’t hold people to standards you invent but aren’t found in Scripture, and never, ever pretend to know another person’s thoughts - THAT is unbiblical judging.