The children of Jacob, or Israel, had been in Egypt for nearly four hundred years. Then God declared that their time of estrangement was finished. He led them to the land he had promised to Abraham, the grandfather of Jacob.
But the Israelites had not had many revelations from God. They hardly knew God. True, they had their traditions and they still feared God, as you can tell from the story of Moses' parents. But they had no frequent voices speaking to them and they had no Bible scrolls.
On this occasion God shows himself to Moses. He must tell the Israelites that the God of their fathers has spoken. Then they will be reminded that God has not forgotten his promises. But from this time on, the Israelites would also know God by a new name—Yahweh, explained as "I AM WHO I AM." That name means, I am here and I am alive.