"Forgetting what lies behind and straining forward to what lies ahead..."

I recall reading The Life and Diary of David Brainerd at some point years ago and being rather intimidated by his example of commitment. The author of "The Bewildering Mr. Brainerd" writes "I am sure that none of us have met anyone so wholly given to seeking to live his or her life for the glory of God and the good of the souls of men like David Brainerd." But...

.... At his own admittance, Brainerd was given over to what he calls "melancholy" (what we call "clinical depression"). This is evident from reading any number of passages in the Diary. When you wed this to his own perception of his depravity, internal vileness (as he calls it) and a sense of his sinful disposition, you have a recipe for morbid introspection. From the beginning of his Diary to the end, Brainerd reveals his sense of his own "vileness" (which he refers to 86 times) as the predominant thought in his heart. On Thursday, April 16, 1747—just six months prior to his death—Brainerd wrote,

Was in bitter anguish of soul in the morning, such as I have scarce ever felt, with a sense of sin and guilt. I continued in distress the whole day, attempting to pray wherever I went; and indeed could not help so doing: but looked upon myself so vile, I dared not look any body in the face; and was even grieved that any body should show me any respect, or at least that they should be so deceived as to think I deserved it.

If anyone rightly falls under the just criticism of being morbidly introspective, it is Brainerd.

Second, Brainerd's Lack of Gospel Clarity. Connected to the first, is Brainerd's struggle to see clearly the all sufficent sacrifice of Jesus for the forgiveness [of] sin. A search of the Diary yields the conclusion that Brainerd rarely talked about Christ crucified for the forgiveness of his sins. ....

Joe Rigney, author of Lewis on the Christian Life, writes in "You’re Not Just a Sinner":

When it comes to introspection and self-examination, C.S. Lewis is very mindful of the danger that he associates (and not wrongly) with certain strands of Puritanism. This is a view of the Christian life that says the holier you get, the more self-contempt you’ll have, because you’ll be more aware of the sliminess in your heart. As you grow in holiness, you’ll become more aware of your sinfulness, and that awareness leads you to a low view of self, saying I am a cesspool of sin, there are slimy bogs down deep in my heart. That’s just what I am.

Lewis recognizes that feature of certain strands of Christianity, and says That’s not healthy. Yet he’s very careful because, while he thinks it’s unhealthy, it’s not unhealthy because it’s false. It’s true. You are that bad. In fact, you’re worse than you think. But the fact that you have a cesspool of sin down in your heart doesn’t mean you should camp down there. Indeed, that’s precisely what God is trying to lead you out of.

Lewis commended what he called an “imaginative glimpse.” So, don’t stare at your sinfulness. See it, acknowledge it, be honest about it, and then bring it to God. That sin is what Jesus forgives. That sinfulness is what you have to be transformed out of. ....

The Bewildering Mr. Brainerd | The Christward Collective, You’re Not Just a Sinner | Crossway Articles