'Shepherd' in the Bible

The words of the wise are like [prodding] goads, and these collected sayings are [firmly fixed in the mind] like well-driven nails; they are given by one Shepherd.

But beyond this my son, [about going further than the words given by one Shepherd], be warned: the writing of many books is endless [so do not believe everything you read], and excessive study and devotion to books is wearying to the body.