It is surprising to think that God's Kingdom would contain bad as well as good people. but Jesus warned about it in the parable of the wheat and the tares. He wants us to know that there are false preachers in the church who are in it for their own gain. Many even bring a false gospel.
We are to be diligent in our study of the Scriptures because they will remain with us until the end of time. Then, Jesus will bring the separation.
Know what you believe and stand on the truth.