Interesting question. Let me paraphrase it: “How can I know when I listen to a man preach if he is really a Christian or not?” The answer boils down to this. Listen to what he preaches. His preaching reveals his heart and his heart reveals his theology. That’s what Jesus meant when he said, “By their fruits you will know them” (Matthew 7:20). The “fruit” of a teacher is his teaching.  Now it’s more than that, obviously, but the teaching itself is where you must begin. So as you listen, you must ask some questions:

Are the sermons based on the Word of God?
Does he preach the gospel of Christ?
Does his preaching exalt the man or the Lord Jesus Christ?
Does the preaching promote holiness of life?

The answers may not be quickly seen, but if you listen long enough, the truth will come out.

Then there is the life of the minister. It can be much harder to draw conclusions about this. But you ask yourself, “Does he live in a manner consistent with what he preaches?”

Now is it possible that a man might pass the theology test and the lifestyle test, only later to be revealed as a hypocrite? Yes, that does happen from time to time. Our occasional disappointments in others should not cause us to doubt all spiritual leaders. But if we are careful and thoughtful in our evaluation, we can have confidence that those who teach the Word of God truly know the Lord. Remember that “the Lord knows those who are his” (2 Timothy 2:19). We may not always be certain about the salvation of others. But the Lord truly does know. When we are uncertain, he remains absolutely certain about his children on the earth.

See The Life God Blesses.