Whoever learns from man does not receive knowledge immediately from the intelligible species which are in his mind, but through sensible words, which are signs of intelligible concepts. Now as words formed by a man are signs of his intellectual knowledge; so are creatures, formed by God, signs of His wisdom. Hence it is written (Sirach 1:10) that God "poured" wisdom "out upon all His works." Hence, just as it is better to be taught by God than by man, so it is better to receive our knowledge from sensible creatures and not by man's teaching.
Thomas Aquinas, ST III.12.3 ad 2
