Isa 49:6, Isa 56:6-7, Isa 60:2-3, Acts 13:46-48, Eph 2:12-13
In the Old Testament, King Solomon prayed that the Gentiles would also believe in God. (2 Chron 6:32-33)
2 Chron 6:32 Moreover concerning the stranger, which is not of thy people Israel, but is come from a far country for thy great name's sake, and thy mighty hand, and thy stretched out arm; if they come and pray in this house; 33 Then hear thou from the heavens, even from thy dwelling place, and do according to all that the stranger calleth to thee for; that all people of the earth may know thy name, and fear thee, as doth thy people Israel, and may know that this house which I have built is called by thy name.
In the Old Testament, it was prophesied that God would save not only those who were preserved in Israel, but also the Gentiles. (Isa 49:6, Isa 56:6-7, Isa 60:2-3)
Isa 49:6 And he said, It is a light thing that thou shouldest be my servant to raise up the tribes of Jacob, and to restore the preserved of Israel: I will also give thee for a light to the Gentiles, that thou mayest be my salvation unto the end of the earth.
Isa 56:6 Also the sons of the stranger, that join themselves to the Lord, to serve him, and to love the name of the Lord, to be his servants, every one that keepeth the sabbath from polluting it, and taketh hold of my covenant; 7 Even them will I bring to my holy mountain, and make them joyful in my house of prayer: their burnt offerings and their sacrifices shall be accepted upon mine altar; for mine house shall be called an house of prayer for all people.
Isa 60:2 For, behold, the darkness shall cover the earth, and gross darkness the people: but the Lord shall arise upon thee, and his glory shall be seen upon thee. 3 And the Gentiles shall come to thy light, and kings to the brightness of thy rising.
All Gentiles who believed in Jesus as the Christ were saved. (Acts 13:46-48, Ephesians 2:12-13)
Acts 13:46 Then Paul and Barnabas waxed bold, and said, It was necessary that the word of God should first have been spoken to you: but seeing ye put it from you, and judge yourselves unworthy of everlasting life, lo, we turn to the Gentiles. 47 For so hath the Lord commanded us, saying, I have set thee to be a light of the Gentiles, that thou shouldest be for salvation unto the ends of the earth. 48 And when the Gentiles heard this, they were glad, and glorified the word of the Lord: and as many as were ordained to eternal life believed.
Ephesians 2:12 That at that time ye were without Christ, being aliens from the commonwealth of Israel, and strangers from the covenants of promise, having no hope, and without God in the world: 13 But now in Christ Jesus ye who sometimes were far off are made nigh by the blood of Christ.