You cannot search your heart too diligently, for self-righteousness is the subtlest enemy of all. Beware of thinking, as the devil would have you, that the parable of the Pharisee and the tax collector is a very good one for everybody else, but does not exactly touch your case.
Be sure in this way you will lose your own souls. Know for a certainty, if you never groan under the burden of sin and never make the tax collector’s prayer your own, you cannot be saved. And if you feel this minute any doubt about your salvation, it were far better to give your soul the benefit of it, and re-lay the foundation of your faith.
~ J.C. Ryle