You can translate this in an active form. Alternate translation: "they can know about God because of what they can plainly see" (See: [[rc://en/ta/man/jit/figs-activepassive]])
Here "enlightened them" means God has shown them the truth about him. Alternate translation: "Because God has shown everyone what he is like" (See: [[rc://en/ta/man/jit/figs-explicit]])