>> The Bible says that the heart is “deceitful above all things and desperately wicked, who can know it?”
The Bible *also* includes three epistles of John, the first of which lays out a lot of good background information about your question, if not a black-and-white answer to it.
Read it all, but for the sake of a pithy quotable verse: :-)
“I write these things to you who believe in the name of the Son of God that you may know that you have eternal life.” (5:13)
So one can know for themself, but not if the preacher in the pulpit is truly saved?
But What John wrote only applied to those who truly believed. Who didn’t believe, but thought they did?