Bede

A shrewd man conceals knowledge. Shrewd in this place is understood in a good sense, that is, wise and prudent, who sometimes conceals his knowledge out of prudence: for two reasons, either not being able to speak to weak listeners as to spiritual ones, but as to carnal ones, or being unwilling to give what is holy to the dogs, nor to cast pearls before swine.

Commentary on Proverbs ↗