This can be stated in active form. Alternate translation: "things that we can see ... things that we cannot see ... things that we cannot see" (See: [[rc://en/ta/man/jit/figs-activepassive]])
You can supply the verb for this phrase. Alternate translation: "but we are watching for things that are unseen" (See: [[rc://en/ta/man/jit/figs-ellipsis]])