Jerome : (Verse 6) And he shall be left like a cluster of grapes, like the shaking of an olive tree, with two or three berries on the top of the branch, or four or five on its fruitful branches, says the Lord God of Israel. Those who are chosen because of their humility are like grain on the threshing floor and grapes in the vineyard, that are saved: and like the shaking of the olive tree, whether two, three, four or five olives. For when the stroke of the Jewish people came, that olive tree of the people of Israel, which under Moses had six hundred thousand armed men (Num. 26), and under David, counted by Joab, an innumerable people (2 Sam. 24), could hardly offer a few fruits to the Lord and Savior: Paul and Barnabas two olives, and Peter and James, and John (Acts 13), who also saw the transfigured Lord on the mountain and deserved to go with the Lord to the house of the synagogue official's daughter (Matt. 17). But four and five olives make up the remaining nine Apostles, in whom Matthias took the place of the treacherous Judas, who, for some unknown reason, was separated into four and five olives, in order to demonstrate the number of the Gospels and the volumes of the Law within themselves, as if they were proclaimers of both Instruments (Acts 1). — Commentary on Isaiah