Honestly, when you get all tangled up with your Israel, gentiles, new man, and your boundaries for sectioning off what is to be read as scripture and what isn't, you get lost.
First, as we read scripture we need to know who inspired it, what that inspiration consists of. What are the governing principles of the Lord? Then we look to see how a specific scripture expresses those principles, and we cannot assign something to the Lord that is out of His character.
From the first pages of scripture, we find the Lord created all man, and wants all men to be forgiven their sins so they can live forever with Him. n God set up the sacrificial system for this purpose, to keep the saints until Christ came.
God did not want the nations of the old testament to die of their sins, God hoped they would see His glory and righteousness through seeing it in the Hebrews he tried to train to express that. God did not want your "Israel only", God is the same God for the gentiles who rejected Him, as God is the God for the current Jews who think the Messiah is yet to come, just as He is the God of the saints.