Q. Re: Old Testament Promises. You raise a valid and interesting point. Question is why the church fathers chose to include promises made to Israel in the canon to be read by the church.
A. Paul gave us the answer to that.
For everything that was written in the past was written to teach us, so that through the endurance taught in the Scriptures and the encouragement they provide we might have hope (Romans 15:4), and
All Scripture is God-breathed and is useful for teaching, rebuking, correcting and training in righteousness, so that the servant of God may be thoroughly equipped for every good work (2 Tim. 3:16-17).
We can and should learn from God’s dealings with Israel, because doing so helps us know more about Him and avoid repeating their mistakes.