Adam Clarke on Psalms 19:12

Who can understand his errors? - It is not possible, without much of the Divine light, to understand all our deviations from, not only the letter, but the spirituality, of the Divine law. Frequent self-examination, and walking in the light, are essentially necessary to the requisite degree of spiritual perfection.

Cleanse thou me from secret faults - From those which I have committed, and have forgotten; from those for which I have not repented; from those which have been committed in my heart, but have not been brought to act in my life; from those which I have committed without knowing that they were sins, sins of ignorance; and from those which I have committed in private, for which I should blush and be confounded were they to be made public.