Psalms 32:9

Psalms 32:9. Be ye not as the horse, or as the mule, which have no understanding: whose mouth must be held in with bit and bridle, lest they come near unto thee.

Do not be difficult to manage. Be not hard-mouthed. Be ready to be guided by the eye of God. Be not like stubborn beasts, that must be held in with bit and bridle, and that often need the whip, too.