Here is how I see the relationship now.
There <i>is</i> one chosen line that has the promise that their seed will be preserved until the end of the earth. This is also the family line that has the <i>right</i> to the priesthood by lineage. (Others have the priesthood too, but this one line has a right to it, they are “lawful heirs.”)
This promise went from Adam to Seth to Enos, down to Enoch, then on to Noah, and finally to Abraham. Then it was given to Isaac, then to Jacob. I had wondered if it broadened out at that point to include all of his 12 sons. We call all of Israel a “chosen people” and Isaiah reminds them that God will never destroy them completely. However, Genesis 45 and 2 Ne 25:21 make it clear enough to me that Joseph inherited this blessing next. From there I’m not sure where it goes, but I think there is still one father-to-son line. Well, more than “think” there is, I think it’s clear from scriptures on Joseph Smith that he is of that line too (D&C 86:8-11 for example). I just don’t have any idea if that line is mentioned in scripture between Joseph and Joseph! Though I’m sure it is. I just need to go look and see. 🙂
So there is one “chosen line” still that must remain until the end of the world. Why, exactly? I’m not sure yet. I’m working on that. 🙂
How do we fit into that? Well, I used to wonder if the sealing ordinance, or even baptism itself, meant that we were receiving the blessings originally meant only for the chosen line. I don’t think that is the case anymore. I think that we receive <i>some</i> of those blessings, but not all of them. Just like the whole house of Israel was a chosen people, but Joseph still received THE promise. I think when we are baptized we become counted Abraham’s seed, but he had lots of children even in his lifetime who were his seed but not the chosen son. We are seed like that. We are his seed that fulfills the promise he had that his posterity would number like the stars or the sand. We fulfill that. And we <i>are</i> part of the promise then. We are Abraham’s family. And that comes with blessings. But, we are not the one chosen line that will remain until the end of the world. There is still one family that is fulfilling <i>that</i> part of the promise.
But what is it that we receive? Why are we part of Abraham?
Well I’m thinking back to Abraham 2:9-11:
And I will make of thee a great nation, and I will bless thee above measure, and make thy name great among all nations, and thou shalt be a blessing unto thy seed after thee, that in their hands they shall bear this ministry and Priesthood unto all nations;
And I will bless them through thy name; for as many as receive this Gospel shall be called after thy name, and shall be accounted thy seed, and shall rise up and bless thee, as their father;
And I will bless them that bless thee, and curse them that curse thee; and in thee (that is, in thy Priesthood) and in thy seed (that is, thy Priesthood), for I give unto thee a promise that this right shall continue in thee, and in thy seed after thee (that is to say, the literal seed, or the seed of the body) shall all the families of the earth be blessed, even with the blessings of the Gospel, which are the blessings of salvation, even of life eternal.
All of Abraham’s seed, whether the chosen line or not, will “bear this ministry and Priesthood unto all nations.”
And, all who receive this Gospel are accounted Abraham’s seed.
So, when we are baptized we become Abraham’s seed, whether we were before that or not.
We have a duty and a right to bear this ministry and Priesthood to everyone not (yet) of Abraham’s family.
When we are sealed, what changes? I am not sure, but if nothing else we increase Abraham’s family because when we bear children they are already “born in the covenant.” Or, I wonder if sealing is not a “sealing up” of the family relationship formed first in baptism. Just as birth into a family is not permanent until sealed, I wonder if baptism into the church and therefore into Abraham’s family is not sealed until the sealing ordinance? In addition, I think the sealing ordinance opens up the potential for us to be like Abraham – not in that we have a chosen seed, like him and others in that line – but in that we can have seed that number like the stars and sand (and remember that this is talking about those “in the world and out of the world” as D&C 132 puts it). It also means perhaps that we become like Abraham in that we have the Priesthood and we teach it to our own kids, who then teach it to the world and also enter the temple to be like Abraham, and then they teach it to their kids who preach it to the world but also enter the temple to become like Abraham, and so on…