Has the sun done anything for me? No; he warms me with his rays, and it is by his light that I see you—nothing more.
Maximilien gropes for words to explain why he trusts the Count, and he lands on a tender metaphor. The sun doesn’t “do” favors; it simply lets life be seen. That’s what Monte Cristo has been to him—a light rather than a creditor. Emotionally, the comparison enlarges love’s vocabulary: to see someone clearly is itself a gift. It also hints at the Count’s unseen work on their behalf. Readers feel the warmth of gratitude braided with romance.