Lk 21:24, Isa 59:20-21, Isa 27:9, Jer 31:33
In the Old Testament, it was promised that God would forgive and restore Israel from their sins. (Isa 59:20-21, Isa 27:9, Jer 31:33)
Isa 59:20 And the Redeemer shall come to Zion, and unto them that turn from transgression in Jacob, saith the Lord. 21 As for me, this is my covenant with them, saith the Lord; My spirit that is upon thee, and my words which I have put in thy mouth, shall not depart out of thy mouth, nor out of the mouth of thy seed, nor out of the mouth of thy seed's seed, saith the Lord, from henceforth and for ever.
Isa 27:9 By this therefore shall the iniquity of Jacob be purged; and this is all the fruit to take away his sin; when he maketh all the stones of the altar as chalkstones that are beaten in sunder, the groves and images shall not stand up.
Jer 31:33 But this shall be the covenant that I will make with the house of Israel; After those days, saith the Lord, I will put my law in their inward parts, and write it in their hearts; and will be their God, and they shall be my people.
When the Gentile times are fulfilled, the remnant of Israel will return to God. (Lk 21:24, Rom 11:25-27)
Lk 21:24 And they shall fall by the edge of the sword, and shall be led away captive into all nations: and Jerusalem shall be trodden down of the Gentiles, until the times of the Gentiles be fulfilled.
Rom 11:25 For I would not, brethren, that ye should be ignorant of this mystery, lest ye should be wise in your own conceits; that blindness in part is happened to Israel, until the fulness of the Gentiles be come in. 26 And so all Israel shall be saved: as it is written, There shall come out of Sion the Deliverer, and shall turn away ungodliness from Jacob: 27 For this is my covenant unto them, when I shall take away their sins.