Who is Israel
Some say that it is the Jews or that the Church is Israel (spiritual Israel) and has replaced Israel. Others say the Nation of Israel in the Land of Israel is Israel. Still others say that Israel is Judah and Ephraim reunited.
Then revolving around these perceptions are, respectively, the views of some that the first covenant was done away with and replaced with a New Covenant. Or that both covenants are valid, but one is for the Jews, and the other for the Church; or that both the first and last covenants were given to Israel, and for Israel, and that the Church was never given any covenant.