Matthew Henry
When it is said the land had rest eighty years
, some think it meant chiefly of that part of the land which lay eastward on the banks of Jordan, which had been oppressed by the Moabites; but it seems, by this passage here, that the other side of the country which lay south-west was in that time infested by the Philistines, against whom Shamgar made head.
he delivered Israel; how great the distress was Deborah afterwards related in her song (Judg 5:6), that
in the days of Shamgar the highways were unoccupied, etc.; that part of the country which lay next to the Philistines was so infested with plunderers that people could not travel the roads in safety, but were in danger of being set upon and robbed, nor durst they dwell in the unguarded villages, but were forced to take shelter in the fortified cities.
a plough-share. It is probable that he was himself following the plough when the Philistines made an inroad upon the country to ravage it, and God put it into his heart to oppose them; the impulse being sudden and strong, and having neither sword nor spear to do execution with, he took the instrument that was next at hand, some of the tools of his plough, and with that killed so many hundred men and came off unhurt. See here,