The fear of Hashem is the start of knowledge; fools despise wisdom and instruction.
Rashi compares having proper awe of G-d to terumah, the portion of produce given to a kohein. (The word “reishis” in our verse can mean “the start of,” or it can refer to those priestly gifts.) Like terumah is of one’s best produce, awe of G-d is the finest portion of one’s knowledge. Before one can truly acquire knowledge, he must first have awe of G-d and open his heart to be receptive to wisdom. Fools who have no regard for G-d cannot hope to internalize these messages.