This is an idiom. The heart refers to all of one's emotions, feelings, desires, and will. Alternate translation: "with all my being" or "with everything in me" or "sincerely" (See: [[rc://en/ta/man/translate/figs-idiom]])
Here to disobey God's commandments is described as straying off a path. Alternate translation: "Do not let me disobey your commandments" (See: [[rc://en/ta/man/translate/figs-metaphor]])