The promises were made to Abraham and to his offspring. He did not say, "and to descendents," as if to many, but instead, as if to one, he said, "and to your offspring," who is Christ.
And indeed, for a few days and according to their own wishes, they instructed us. But he does so to our benefit, so that we may receive his sanctification.
Therefore, it is fitting for him to be made similar to his brothers in all things, so that he might become a merciful and faithful High Priest before God, in order that he might bring forgiveness to the offenses of the people.