Adam Clarke on Psalms 32:9

Be ye not as the horse or as the mule - They will only act by force and constraint; be not like them; give a willing service to your Maker. "They have no understanding;" you have a rational soul, made to be guided and influenced by reason. The service of your God is a reasonable service; act, therefore, as a rational being. The horse and the mule are turned with difficulty; they must be constrained with bit and bridle. Do not be like them; do not oblige your Maker to have continual recourse to afflictions, trials, and severe dispensations of providence, to keep you in the way, or to recover you after you have gone out of it.