Set them on fire. This is a continuation of the concluding picture of the preceding verse. A tree whose branches are stripped of leaves (v. 10) withers and dies. The wood becomes dry. The branches are then cut down and used for firewood. The figure is similar to that of Eze. 31:12, 13, where the fall of Assyria is compared to a tree whose branches have fallen. John the Baptist and Jesus both compared the wicked to trees that were cut down and cast into the fire (Matt. 3:10; John 15:6). Paul compared the literal Jews to natural branches cut off and replaced by the grafted branches of the church (Rom. 11:12-20).