John Calvin Commentary Isaiah 56:8

"The Lord Jehovah, who gathereth the outcasts of Israel, saith, Yet will I gather [others] to him, besides his own that are gathered." — Isaiah 56:8 (ASV)

The Lord Jehovah saith. Isaiah again confirms what he previously testified regarding the restoration of the people. For although he praised in lofty terms the grace of God, by which he would deliver his people, yet the condition of the Church was such that promises of this kind appeared to be ridiculous. Such repetitions, therefore, are not superfluous but were necessarily added to strengthen weak minds, so that they might be fully convinced of what was otherwise incredible.

Who gathereth the outcasts of Israel. It is with reference to the current subject that he gives God this title, for it is his role to gather a scattered church, and the same words, he gathereth the outcasts of Israel, are used here in the same sense (Psalms 147:2). Thus he promises that he will assemble them, and not only them, but that he will also add to them various “peoples,” so that the Church may be very greatly increased and multiplied. Therefore, whenever various calamities of the Church lead us to doubt his gathering them together, we should interpose this shield: “It belongs to the Lord to gather the dispersed of Israel; and, though they are widely dispersed and scattered, yet he will easily and perfectly restore them.”

Still more will I gather upon him his gathered. I willingly keep to the literal meaning of the words of the Prophet. על (gnal) that is, “To” or “Upon”; for he appears to me to have in view what he had said in the previous verse, that the temple would be opened to all peoples, and he means that he will yet add many others to the Jews who have been gathered. This actually happened, for not only did he gather the dispersed in Babylon, but he also gathered other dispersions, which were frequent and occurred almost daily. Nor has he ever ceased to gather, so that he has added a large mass to those who have been gathered.