Charles H. Spurgeon on Psalms 44:21

Shall not God search this out? Could such idolatry be concealed from him? Would he not with holy indignation have detected unfaithfulness to itself, even had it been hidden in the heart and unrevealed in the life? For he knoweth the secrets of the heart. He is acquainted with the inner workings of the mind, and therefore this could not have escaped him. Not the heart only which is secret, but the secrets of the heart, which are secrets of the most secret thing, are as open to God as a book to a reader. The reasoning is that the Lord himself knew the people to be sincerely his followers, and therefore was not visiting them for sin; hence, then, affliction evidently came from quite another cause.