Jude 1:22 (ESV)

22 And have mercy on those who doubt;

Doubting God is about all I can do by nature. I am a sinner. When one starts doubting, his very doubt is an expression of some level of belief. If he did not believe a bit, the doubt would not bother him: the presence of the doubt is itself an indication of concern. Let us not rebuke doubt. Embrace with compassion our doubting brethren, that we might—in obedience to what Jude is saying—build up one another upon the most holy faith.1

John McKnight