Let's start with a pair of Old Testament text and then a couple of texts from the New Testament.
Genesis 17:1-5
1 Now when Abram was ninety-nine years old, the LORD appeared to Abram and said to him, "I am God Almighty; Walk before Me, and be blameless. 2 "I will establish My covenant between Me and you, And I will multiply you exceedingly." 3 Abram fell on his face, and God talked with him, saying, 4 "As for Me, behold, My covenant is with you, And you will be the father of a multitude of nations. 5 "No longer shall your name be called Abram, But your name shall be Abraham; For I have made you the father of a multitude of nations.
Exodus 19:1-6
1 In the third month after the sons of Israel had gone out of the land of Egypt, on that very day they came into the wilderness of Sinai. 2 When they set out from Rephidim, they came to the wilderness of Sinai and camped in the wilderness; and there Israel camped in front of the mountain. 3 Moses went up to God, and the LORD called to him from the mountain, saying, "Thus you shall say to the house of Jacob and tell the sons of Israel: 4 'You yourselves have seen what I did to the Egyptians, and how I bore you on eagles' wings, and brought you to Myself. 5 ~'Now then, if you will indeed obey My voice and keep My covenant, then you shall be My own possession among all the peoples, for all the earth is Mine; 6 and you shall be to Me a kingdom of priests and a holy nation.' These are the words that you shall speak to the sons of Israel."
Matthew 28:18-20
18 And Jesus came up and spoke to them, saying, "All authority has been given to Me in heaven and on earth. 19 "Go therefore and make disciples of all the nations, baptizing them in the name of the Father and the Son and the Holy Spirit, 20 teaching them to observe all that I commanded you; and lo, I am with you always, even to the end of the age."
Romans 1:1, 25-32
I say then, God has not rejected His people, has He? May it never be! For I too am an Israelite, a descendant of Abraham, of the tribe of Benjamin...... 25 For I do not want you, brethren, to be uninformed of this mystery—so that you will not be wise in your own estimation—that a partial hardening has happened to Israel until the fullness of the Gentiles has come in; 26 and so all Israel will be saved; just as it is written, "The Deliverer will come from Zion, he will remove ungodliness from Jacob. 27 This is My covenant with them, when I take away their sins." 28 From the standpoint of the gospel they are enemies for your sake, but from the standpoint of God's choice they are beloved for the sake of the fathers; 29 for the gifts and the calling of God are irrevocable. 30 For just as you once were disobedient to God, but now have been shown mercy because of their disobedience, 31 so these also now have been disobedient, that because of the mercy shown to you they also may now be shown mercy. 32 For God has shut up all in disobedience so that He may show mercy to all.
1 Peter 2:4-10 ESV
4 And coming to Him as to a living stone which has been rejected by men, but is choice and precious in the sight of God, 5 you also, as living stones, are being built up as a spiritual house for a holy priesthood, to offer up spiritual sacrifices acceptable to God through Jesus Christ...... But you are a chosen race, a holy priesthood, a holy nation, a people for God's own possession, so that you may proclaim the excellencies of Him who has called you out of darkness into His marvelous light; 10 for you once were not a people, but now you are the people of God; you had not received mercy, but now you have received mercy.
These passages speak of salvation in corporate, or "national" terms. We might reasonably say God does what He's promise one person at a time (individually) but given the passages above (and there are many others like them in scripture) we cannot say God is saving ONLY individuals. Nor should we construe God's salvation of the individual to be something occurring exclusive of God saving of "the nations," or from the very beginning having a plan to build a nation, a nation of priests (which, according to the 1 Peter 2 text, has already begun).
One other point (for now). In modernity we tend to think of the word "nation" in terms of geo-political nation-state status. We may also think of any mention of "the nation Israel" as something existing genetically, or via bloodline (that is the way the Jews thought about it). Ancient cultures were tribal, and a "nation" was a set of tribes connected via bloodline and/or marriage. Because inter-marriage was prohibited for the Jews, their "nation" was bloodline.
Neither is what God meant when it came to the covenant promise(s) that is Jesus. Jesus is the seed promised Abraham and one of the many things entailed in that promise was the making of many nations, later clarified (or added) was the nation of priests. In other words, nationality is a function of priestly ontology, or theological. That is what it means to be saved from sin. To be saved from sin and wrath is to be a royal priest, a member of God's holy - separate and sacred - nation.