This expression refers to the person who would bring salvation—the infant Jesus—whom Simeon was holding. AT: "the savior whom you sent" or "the one whom you sent to save" (See: [[rc://en/ta/man/translate/figs-metonymy]])
This metaphor means that the child will help people to understand God's will. The Gentiles understanding God's will is spoken of as if it were people using physical light to see a solid object. You may need to make explicit what it is that the Gentiles will see. AT: "This child will enable the Gentiles to understand God's will as light allows people to see clearly" (See: [[rc://en/ta/man/translate/figs-metaphor]] and [[rc://en/ta/man/translate/figs-explicit]])