John of Japan,
Who is in the New Covenant is very relevant.
Are church members in the New Covenant?
Is the new covenant made with gentiles?
Finally you find a chapter in There Really Is a Difference, by Renald Showers (1990), but hey, that is a comparison of dispensationalism and covenant theology, so he would have a chapter when most ignore the discussion--because it's just not that relevant!
In short, you are making a big mountain out of a small molehill.
Who is in the New Covenant is very relevant.
Are church members in the New Covenant?
Is the new covenant made with gentiles?