Matthew Henry on Judges 3:31

The side of the country which lay south-west, was infested by the Philistines. God raised up Shamgar to deliver them; having neither sword nor spear, he took an ox-goad, the instrument next at hand. God can make those serviceable to his glory and to his church's good, whose birth, education, and employment, are mean and obscure. It is no matter what the weapon is, if God directs and strengthens the arm. Often he works by unlikely means, that the excellency of the power may appear to be of God.