The “us” Paul is speaking about are the legitimate children of Israel. Why else would he call these “gentiles” the fleshly children of Abraham
He’s talking about the words and promise made to Abraham. Paul says it’s for “us”. This is why The Church, Christianity, is now ‘Israel’. It’s for all who believe.
24 but also for us.
It shall be imputed to us who believe in Him who raised up Jesus our Lord from the dead,25 who was delivered up because of our offenses, and was raised because of our justification.