They had the old covenant. This was a covenant between them and God. It was not between God and the whole world in this way, yet somehow they could have hope because Abraham, the patriarch in faith, was told that all the families would know God, and that his seed would number so large it would be like the stars or grains of sand.
So they knew this was destined for greatness.
But when? Oh, poor Jacob! Poor forefathers in faith! They were committed to bondage. But God, the God who brought them out of Egypt, was God of Heaven and Earth. There was no failure in Him or deceit in His Word. They were given the Law of Moses, and made into a great nation. They failed many times as they fell into harlotry, idolatry, losing their way.
Of course, if a man were to see their way of life and desired to join the nation following God, he wasn’t disallowed. But this nation, word of this nation’s moral code and belief in God did spread, and the hearts of the pagans were softened. And it is at a wonderfully perfect time in history that our Lord came and made Jew and Gentile one. The rest is history–and our future. There are stages and steps in the history of the world, but we can trust in God’s loving providence.