First be sure you understand the covenants well. As a baptist I didn't.
The church, believers are Israel.
not all of Israel is Israel is because some of spiritual Israel is Gentiles.
So all Israel shall be saved this is by the ingathering of all the elect of al nations.
Gentiles are graft into Israel. The Jews who were broken off branches can be graft back into Israel as well.
Israel is used more than one way in the NT. So is Jew, House of Israel, etc.
Israel was a type. There were physical temporal promises to the ethnic Jews and there were promises to the spiritual or elect Israel. Rom 9.
A Jew is not one who is one outwardly, but one who is one inwardly.
So the promises were not just to ethnic Jews but to those who are JEws by faith, elect. Heirs of Abraham from all nations. Heirs by faith not be ethnicity.
1 7:13-14 What on earth can this possibly mean unless there is a visible external covenant or holiness, being in Israel as an unconverted child was the same as being in the church as a child. We are all called the Children of God, People of God, My People etc. and yet not all are in the invisible covenant or C of Grace,
If there was a sign given to children of believers in the OT then what is the sign in the NT of being in the visible covenant.
There are lots of articles online and threads on this here that have all the facts one needs to see that if there had been a change such that the promise was no longer to believers and their seed, that the mothers would have had an outcry saying how can this be a better covenant if my children are not included any more.
Read the NT as if you were a Jew or a Gentile familiar with Judaism and it was teaching you.
What would you think?
Check out, as for me and my household we will serve the Lord.
Regardless of whether the others believe God works through heads of households. So when a head believes the whole family was circumcised in the OT and in the NT the whole family was baptized.
They receive the benefits of being in the visible covenant. What profit is their being a JEw??? Same as being a child in the covenant today. Check the passage to see what the benefits are.
There is no short proof text, but there is plenty of info thoughout the scriptures if you take the time to study all these things.