John Gill Commentary Psalms 56:3

"What time I am afraid, I will put my trust in thee." — Psalms 56:3 (ASV)

What time I am afraid
It was a time of fear with him now; he was afraid of Achish king of Gath, (1 Samuel 21:12) ; so believers have their times of fear;

about their interest in the love, and grace, and covenant of God; about their sins and corruptions, and the prevalence of them, fearing they shall perish by them; and about their enemies, who are many, lively, and strong;

I will trust in thee ;
trust and confidence in the Lord is the best antidote against fears; who is unchangeable in his love, in whom is everlasting strength, and who is faithful and true to every word of promise; and therefore there is great reason to trust in him, and not be afraid.