“…Help Thou mine unbelief” – Mark 9:24

There are many true believers who at the first are tried with unbelief, because they have now, more than ever they had before, a sense of their past sins. Many a man receives a far deeper sense of sin after he is forgiven than he ever had before. The light of the law is but moonlight compared with the light of the gospel, which is the light of the sun. Love makes sin to become exceeding sinful.

“My Sins, my Sins, my Savior!
How sad on Thee they fall;
Seen through Thy gentle patience,
I tenfold feel them all.

I know they are forgiven,
But still their pain to me
Is all the grief and anguish
They laid, my Lord, on Thee.”

The light of the promise gleaming in the soul reveals the infinite abyss of horror which lies in indwelling sin. In the light of God’s countenance we discover the filthiness, the abomination, the detestable ingratitude of our past conduct…Oh, that we could blot out those evil days! We have said, “Cursed be the sun that it rose on such a day as that in which I so defiled myself with iniquity.” Thus, under a sense of sin, though there is the belief that we are pardoned, there may also arise the unbelief against which we need the Lord to help us…Learn from this that a measure of doubt is consistent with saving faith; that weak faith is true faith, and a trembling faith will save the soul. If thou believest, even though thou be compelled to say, “Help Thou mine unbelief,” yet that faith makes thee whole, and thou art justified before God. ` C.H. Spurgeon

https://www.blueletterbible.org/Comm/spurgeon_charles/sermons/1033.cfm