Adam Clarke on James 1:6

Let him ask in faith - Believing that God IS; that he has all good; and that he is ever ready to impart to his creatures whatever they need.

Nothing wavering - Μηδεν διακρινομενος· Not judging otherwise; having no doubt concerning the truth of these grand and fundamental principles, never supposing that God will permit him to ask in vain, when he asks sincerely and fervently. Let him not hesitate, let him not be irresolute; no man can believe too much good of God.

Is like a wave of the sea - The man who is not thoroughly persuaded that if he ask of God he shall receive, resembles a wave of the sea; he is in a state of continual agitation; driven by the wind, and tossed: now rising by hope, then sinking by despair.