Deuteronomy 19:8-9

If the Lord thy God enlarge thy coast As far as the Euphrates. If thou shalt keep all these commandments This shows that the promise of enlarging their border was conditional, and the condition not being performed the promise was never accomplished, so that there was no need for three more cities of refuge. This the Jewish writers themselves own. “Yet the holy blessed God,” say they, “did not command it in vain, for in the days of Messiah the Prince, they shall be added.” They expect it in the letter: but we know it has in Christ its spiritual accomplishment. For the borders of the gospel Israel are enlarged according to the promise: and in the Lord our righteousness, refuge is provided for all that by faith flee to him.