Any time the Bible talks about Abraham, Isaac, and Jacob together, it is really talking about God's covenant. Covenant, in the biblical sense, is an intimate and intentional word for relationship. It is just as much about the "who" of the covenant as it is about the covenant itself. God loves people. He loves people more than He loves the words that describe His love and relationships with people [like "covenant"]. Take Ex 32.13 and Deut 9.27 as examples.
In these texts, Moses longs for God to remember His covenant promises. But He doesn't say that exactly. He says, "Remember Abe, Isaac, and Jake." He says it like this because God is into relationships. He is into knowing people [Rom 8.29, 1 Cor 8.3, Jer 1.5, Gal 4.9, Mt 7.23] and people knowing Him [Gal 4.9, Jn 17.3]. He is not into random promises. The reason that the Bible uses such pregnant language like “covenant” is because God had to show people the gravity of their sin and need and the “breadth, length, height, and depth” of His love [Eph 3.18].
With all of this in mind, now you can read Romans 9. If you randomly pick out the hard verses, of course you won’t get it. Look at 9.6. “The word God has not failed.” This means His covenant promises stand in spite of ethnic
Here’s the deal. God loves people. And to those who are recipients of His covenant promises and His mercy, He will exert great energies [mercy in 9.15, 16, 23; compassion in 9.15; power in 9.17, 22; wrath in 9.22] in sustaining those relationships. This is His Church. This is His Body. And He does so for glory, His glory [9.23; 8.29-30].