 We can't, can we? Only God knows what's in another person's heart. All we have to go by is the confession of their mouth and their life. And even with those things, we're not always too sure. There have been folks that we thought were pillars of the church that we later found out were phonies. And there have been others that we were convinced were not Christians who later repented of their errors and became fruitful members of the church.