When Yahweh made His covenant with Abraham, He promised an eternal unconditional covenant with Abraham’s descendants (the Israelites). Whilst some of God’s future promises to the children of Israel had conditions, this initial covenant had none. That meant that Yahweh would have to fulfill His promises no matter what!
The promises to Abraham were passed down through Isaac and then Jacob/Israel to Jacob’s twelve sons who became the twelve tribes of Israel. All the promises to the three patriarchs were destined to be fulfilled in these twelves tribes. Everything in the covenants was about them. Furthermore, any additional blessings upon the twelve tribes would only supplement the pre-existing covenant with Abraham, Isaac, and Jacob.