However, it was the Lord's will for him to be crushed and to suffer, for when he gives his life as a guilt offering he will see his descendants, he will have a long life, and what the Lord wants will be achieved through him.
So the promise is based on trusting God. It is provided as a free gift, guaranteed to all the children of Abraham—not merely to those who follow the law, but also to those who trust like Abraham, the father of us all.
In complete contrast, you are a specially-chosen family, a royal priesthood, a holy nation, a people belonging to God. Consequently you can reveal the wonderful things he's done, calling you out of darkness into his marvelous light.