They were Jews, and yet Christian when they believed Jesus was the Messiah.
Written "for" Jews? Exclusively?
I'd enjoy watching you try to prove that.
shalom b'SHEM Yah'shua HaMashiach Adonai
Very specifically: Romans 11 where Paul discusses who is grafted into whom.
NAsbU Romans 11:17 But if some of the branches were broken off,
and you, being a wild olive, were grafted in among them
and became partaker with them of the rich root of the olive tree,
NAsbU Romans 11:19 You will say then, "Branches were broken off
so that I might be grafted in."
Paul warns against the pride of a Gentile follower of Yah'shua.
NAsbU Romans 11:22 Behold then the kindness and severity of God;
to those who fell, severity, but to you, God's kindness,
if you continue in His kindness; otherwise you also will be cut off.
NAsbU Romans 11:23 And they also, if they do not continue in their unbelief,
will be grafted in, for God is able to graft them in again.
A Jew who comes to know the Jewish Messiah for their salvation
does not become a Christian,
They become a "called out one", a member of the Ekklesia.
They become a Messianic Jew.
The L-rd's name ( Shem ) is not je-zeus;
it is Yah'shua ( YHvH is my salvation )
Which is why you must call on His Name for salvation.