Have you ever come across the following passage? It exactly matches the words Christ said in John 3:16 above.
Isaiah 45:17
17 But Israel shall be saved in the Lord with an everlasting salvation: ye shall not be ashamed nor confounded world without end
The promise is for Israel to be an unending world; an everlasting kingdom.
Romans 9:1-5
I say the truth in Christ, I lie not, my conscience also bearing me witness in the Holy Ghost, That I have great heaviness and continual sorrow in my heart. For I could wish that myself were accursed from Christ for my brethren, my kinsmen according to the flesh:
4 Who are Israelites; to whom pertaineth the adoption, and the glory, and the covenants, and the giving of the law, and the service of God, and the promises; Whose are the fathers, and of whom as concerning the flesh Christ came, who is over all, God blessed for ever. Amen.
The Israelites, to whom pertains:
- the adoption
- the glory
- the covenantssssssssss
- the law (notice it's a separate entry)
- the service
- the promisessss
- of whom Christ came in the flesh
Amos 3:1-2
Hear this word that the Lord hath spoken against you, O children of Israel, against the whole family which I brought up from the land of Egypt, saying,
2 You only have I known of all the families of the earth:
The new covenant isn't made with all mankind. It's made with Israelites; with Israel.
But the law has always allowed gentiles to graft into (and become part of) Israel, but everything is for Israel. Everything. The covenants are for them. And in that way "all Israel will be saved", both the wild branches grafted in and the natural branches regrafted. Romans 11.