Therefore wilt he give them up - Jesus Christ shall give up the disobedient and rebellious Jews into the hands of all the nations of the earth, till she who travaileth hath brought forth; that is, till the Christian Church, represented Revelation 12:1, under the notion of a woman in travail, shall have had the fullness of the Gentiles brought in. Then the remnant of his brethren shall return; the Jews also shall be converted unto the Lord; and thus all Israel shall be saved according to Romans 11:26.
Unto the children of Israel - Taking in both families, that of Judah and that of Israel. The remnant of the ten tribes, wherever they are, shall be brought in under Christ; and though now lost among the nations of the earth, they will then not only be brought in among the fullness of the Gentiles, but most probably be distinguished as Jews.
On this verse Abp. Newcome says, "The sense is, God will not fully vindicate and exalt his people, till the virgin mother shall have brought forth her Son; and till Judah and Israel, and all the true sons of Abraham among their brethren the Gentiles, be converted to Christianity.
Therefore - Since God has so appointed both to punish and to redeem, He, God, or the Ruler “whose goings forth have been from of old from everlasting,” who is God with God, “shall give them up, that is, withdraw His protection and the nearness of His Presence, “giving them up:”
(1) into the hands of their enemies. And indeed the far greater part never returned from the captivity, but remained, although willingly, in the enemy‘s land, outwardly shut out from the land of the promise and the hope of their fathers (as in 2 Chronicles 36:17).
God was less visibly present among them. Prophecy ceased soon after the return from the captivity, and many tokens of the nearness of God and means of His communications with them, the Ark and the Urim and Thummim were gone. It was a time of pause and waiting, wherein the fullness of God‘s gifts was withdrawn, that they might look on to Him who was to come. “Until the time that she which travaileth hath brought forth,” that is, until the Virgin who should conceive and bear a Son and call His Name Emmanuel, God with us, shall give birth to Him who shall save them. And then shall be redemption and joy and assured peace. God provides against the fainting of hearts in the long time before our Lord should come.
Then - (And). There is no precise mark of time such as our word then expresses. He speaks generally of what should be after the Birth of the Redeemer. “The remnant of His brethren shall return unto the children of Israel.” “The children of Israel” are the true Israel, “Israelites indeed” John 1:47; they who are such, not in name (Romans 9:6, etc.) only, but indeed and in truth. His brethren are plainly the brethren of the Christ; either because Jesus vouchsafed to be born “of the seed of David according to the flesh” Romans 1:3, and of them “as concerning the flesh Christ came, who is over all, God blessed forever” Romans 9:5; or as such as He makes and accounts and “is not ashamed to call, brethren” Hebrews 2:11, being sons of God by grace, as He is the Son of God by nature. As He says, “Whosoever shall do the will of My Father which is in Heaven, the same is My brother and sister and mother” Matthew 12:50; and, “My brethren are these who hear the word of God and do it” Luke 8:21.
The residue of these, the prophet says, shall return to, so as to be joined with, the children of Israel; as Malachi prophesies, “He shall bring back the heart of the fathers to the children, and the heart of the children to the fathers” (Hosea 1:11; Isaiah 11:10, etc.). This has been fulfilled in each generation since our Lord came, and shall be yet further in the end, when they shall haste and pour into the Church, and so “all Israel shall be saved” Romans 11:26.
But “the promise of God was not only to Israel after the flesh, but to all” also that were afar off, even as many as the Lord our God should call Acts 2:39. All these may be called the remnant of His brethren, even those that were, before, aliens from the commonwealth of Israel and afar off Ephesians 2:12-14, but now, in Christ Jesus, made one with them; all, brethren among themselves and to Christ their ruler.: “Having taken on Him their nature in the flesh, He is not ashamed to call them so, as the Apostle speaketh, confirming it out of the Psalm, where in the Person of Christ he saith, “I will declare Thy name unto My brethren” Psalm 22:22. There is no reason to take the name, brethren, here in a narrower sense than so to comprehend all “the remnant whom the Lord shall call” Joel 2:32, whether Jews or Gentiles. The word “brethren” in its literal sense includes both, and, as to both, the words were fulfilled.