John Gill Commentary Psalms 31:14

"But I trusted in thee, O Jehovah: I said, Thou art my God." — Psalms 31:14 (ASV)

But I trusted in thee, O Lord
His faith revived again under all the discouraging views he had of things, and was exercised upon the Lord; he committed himself to him, believing he was able to help him in his time of trouble, and deliver him;

I said, you [are] my God ;
he claimed his covenant interest in him, and used it as an argument with him to have regard unto him, and as a support to his faith in his present distress; (See Gill on Psalms 7:1).