A damnable sin!
Spurgeon, "THE DANGER OF DOUBTING"
It is my firm conviction, that to doubt the kindness, the
faithfulness, and the love of God, is a very heinous offense.
Unbelief is akin to Atheism--
Atheism denies God's existence.
Unbelief denies God's goodness.
And since goodness is essential to God, these
doubts do, in reality, stab at his very being.
That can be no light sin which makes God a liar; and yet
unbelief does in effect, cast foul and slanderous suspicion
upon the veracity of the Holy One of Israel.
Unbelief of God is the fountain of innumerable sins--
as the black cloud is the mother of many rain-drops,
so dark unbelief is the parent of many crimes.
Unbelief concentrates the vice of ages into a moment,
and gathers up the virus of all the offenses of the
race in one transgression.
Unbelief is a damnable sin, that it should be
by every believer, should be struggled against, should if
possible be subdued, and certainly should be the object
of our deep repentance and abhorrence.