Despite all of Ether's diligence in teaching the Jaredites and prophesying great and marvelous things to them, they still wouldn't believe, because they couldn't see. But they really missed the boat on what faith is and isn't. Seeing isn't faith. If we could see it and prove it then we would have no need for faith. But Moroni steps in and promises us that as we act on our faith, as we live it and take steps of faith THEN we receive a witness, THEN we receive a confirmation of what we believe.