Olive oil gives light through burning. Witnesses testify to what they’ve seen by using their mouths. In this verse these two images are combined so that the words coming from these witnesses’ mouths is a fire consuming their tormentors. The result of this fire is that these foes are killed. (See further Leviticus 10:2; Numbers 16:35; 2 Kings 1:10, 2 Kings 1:12.) The witnesses continue their work in a dramatic way for the whole 1,260 days allotted to them.
5 And if anyone would harm them, fire pours from their mouth and consumes their foes. If anyone would harm them, this is how he is doomed to be killed.