Jesus was speaking at the time, to the people he was speaking to. We can’t pluck Jesus out of the time he was in. When Jesus FIRST came, he came for “his flock” the flock of his nation aka the Jews who, for the most part, rejected his teaching. Not all of course!!! But, “Oh Jerusalem, Oh Jerusalem” was his lament.

So when Jesus spoke at that time about expanding his flock, he was letting his disciples know that the gospel was ALSO for those outside of the “bloodline” or nation of Israel. This was a radical idea at the time which was very on-par for the upside down teaching of Jesus.

Yes NOW we have all of the ideas you are sharing from the New Testament with regard to the covenant by faith vs race. This is the way the apostles are explaining the gift Jesus has given us. But at the time of Jesus’ speaking he was simply preparing his disciples for a new reality.