he is a double-minded man, unstable in all he does."Double minded" is literally "two souled". The soul in the Bible is the seat of affections or desires. It is the wellspring of all that you want. The man of two souls is unstable because he is torn on the inside.
We all struggle with that inner battle. Paul talks about this in Romans 7:14-25, but we need to take this verse in context. This is not talking about a Christian man who is battling the inner man, this is talking about a man who is not steadfast in his faith in Christ. He has never taken that stand of faith. He is a doubter, he expects nothing from the Lord, nor should he.
These are the kind of people that you need to steer clear of. Their instability that is caused by their lack of faith causes them to seek to control everything themselves. This usually leads to actions that have no care or concern for others, and they usually leave a path of destruction behind them.