The body sees what the scheming mind is blind to. The ass is the animal nature, the flesh that carries a person, and it perceives the drawn sword long before the calculating self will admit anything stands in the way. The angel with the sword is the higher power set across a wrong course, the check that cuts through a plan the mind has already justified. So the body turns aside into the field, breaking from the intended road, while the mind beats the very flesh that just saved it, punishing the instinct for refusing to serve the appetite.
The part of a person that reasons toward reward will strike down the honest warning of the body rather than stop. What the flesh flinches from, the greedy mind calls disobedience.
Ass: the animal nature and the body that carries a person, whose plain instinct sees danger before the clever mind will
Angel of the LORD: the higher power standing across a wrong course, the inner check a person cannot argue away
Sword drawn: the cutting force of that check, ready to sever a plan the mind has already excused
The field: the ground off the intended road, the turning aside the body chooses when the way ahead is barred