We Gentiles ARE the nations that the apostles were commanded to go to and make disciples of...however, it is still a word to the church in general.
Which Israel are you speaking of here though, brother? The "Israel of God" or "Israel after the flesh"? Unbelieving Israel after the flesh unfortunately is not salt and light and failed to show God's glory to the world, so sadly they were thrown out and trampled by men in 70AD. It is still a word and warning to the Israel of God (the church) today though.
The "Israel of God" are the believing Jews, as is portrayed in Romans 9-11.
Jeremiah 31:35-37 KJV
35) Thus saith the LORD, which giveth the sun for a light by day, and the ordinances of the moon and of the stars for a light by night, which divideth the sea when the waves thereof roar; The LORD of hosts is his name:
36) If those ordinances depart from before me, saith the LORD, then the seed of Israel also shall cease from being a nation before me for ever.
37) Thus saith the LORD; If heaven above can be measured, and the foundations of the earth searched out beneath, I will also cast off all the seed of Israel for all that they have done, saith the LORD.
Did God cast away His people for something they did?
Do you suppose God rejected His entire chosen nation, or did He leave Himself a remnent? I think He left a remnant. These things are plainly portray in Scripture.
I believe God keeps His promises, and this one is ironclad. The sun and moon are still doing their thing. I've not been to the center of the earth, have you? Have you measured the heavens with a ruler?
I'm thinking not. No one has. And so Israel, the children of Jacob, remain a nation before God even today. It's right there in the Word, the only question is whether we will believe it.
Much love!