Since all true Christians are "contenders with God" they are all "Israelites" really.
It is the context in the Bible that shows which "Israel" is being spoken of in which verse.
Since the 144,000 in Revelation are said to be taken "out of all Israel" it stands to reason that the anointed 144,000 are taken out of all Christians.
In that context, Israel = all Christians.
When Jesus said to the faithful apostles that they would sit on 12 thrones to judge all Israel, he didn't mean the literal nation of Israel, he meant all believers.
Israel = all Christians.
When it says in Revelation that "a great crowd out of all nations and tribes and tongues" joins "Israel", it is talking about non-believers who will be saved, just like there was a great crowd of non-believers who went out of Egypt with the Jews at the end of the tribulation in that day, those who said "we will go with you people, for we have heard that God is with you people".
The Bible is clear that there will be a great crowd of non-believers who survive the great tribulation.