Substitution

Anyone can be in the covenant, and anyone can opt out.  The concept of substitution is Eternal.  It always was, and it always will be.  It is of God.  There is no absolutes until the end.  The end, the final judgment, or the resurrection seals all covenants made in mortality.  It marks the end of this stage of existence.  But, prior to the end everything is changeable.  Promises, or covenants are made, and God always keeps His promises, but each one is contingent on our keeping them.  Thus, until "the end" nothing is permanent, fixed, or Eternal -- except God, and the covenants themselves.

The Firstborn

We think of the "Patriarchal Order" as absolute.  The authority of a father, and all his wealth and power, are passed down to the firstborn son.  However, this doesn't seem to be universal.

As Lehi is giving his final words to his sons, he turns to one of his younger sons, Jacob, and calls him his "firstborn" three times.  The full term he uses is "firstborn in the wilderness."  He takes his first blessing away from his oldest sons and gives it to Nephi, but calls Jacob his "firstborn."  Now, if we look at the subsequent events in the lives of these, what we see is that for hundreds of years the children of Nephi are the kings of the faithful people of Lehi, but the children of Jacob are the prophets we read in the Book of Mormon.  We know of no children of Nephi for almost 400 years.  Jacob, has essentially become a substitute for the firstborn of Lehi, taking the role of the prophet, or patriarch, and passing that authority down through his generations.  He specifically states that his brother, Nephi, gave him that authority.

When Abraham was talking with the Lord and Ishmael was a teenager he said, "I wish Ishmael had an interest in knowing thee."  Apparently Ishmael wasn't interested in the things of the Lord as Abraham was.  The Lord told him that there would be another, born of his first wife, Sarah, who would fulfill the promise.  Thus, though Isaac wasn't the firstborn of Abraham, he was always called this because he fulfilled the covenant of the patriarchal order of Abraham.

Perhaps this is an illustration of things in Heaven.  Abraham represents the Father.  Ishmael represents Lucifer.  Isaac represents Jehovah. Let's say that Lucifer, a "son of the morning," is really the firstborn of the Father, but refuses the covenant.  Each apparently had the option of being the "Only Begotten" of the Father.  Lucifer contended for the position saying, "here am I, send me, I will be thy son, and I will redeem all mankind, that one soul shall not be lost, and surely I will do it; wherefore give me thine honor."  (Moses 4:1)  But he was not chosen.  Jehovah, then, fulfilled the covenant of the Messiah by saying, "Father, thy will be done, and the glory be thine forever."  (Moses 4:2)  He became the "Firstborn" by making and keeping the covenant of "the chosen One."

"So the last shall be first, and the first last: for many be called, but few chosen."  (Matthew 20:16)  Does this Scripture refer to Christ?  All of them do.  There are many who are called, who receive the promise and make covenants with God.  However, those who are selfish, self-seeking, wanting power, glory, and honor without actually fulfilling the promise are not chosen.  Only those who fulfill their covenants actually fill a position of glory in the Eternities of power, glory, honor, and Eternal Lives, forever and ever.  Jesus fulfilled His promise, the covenant, or as He said, "I partook and finished my preparations unto the children of men."  (D&C 19:19)  He did the work of the Firstborn.

This concept is found throughout the scriptures -- Jacob is called the "firstborn" of Isaac, and Joseph is called the "firstborn" of Jacob, though neither of them really were.  Then, Jacob is renamed "Israel" and carries the promise with him that "all the families of the Earth will be blessed through his name."  This refers to the Messiah being born of his children, but also that everyone who makes a covenant with God becomes his child.

Families are forever

It turns out that the concept of "family" is so ambiguous in this world because the true family is the family of God.  People can "opt in" to the family of God through the covenants of the Gospel of Jesus Christ.  They can become His "children" and become the "firstborn" of Jesus, though they have no connection at all physically or genetically.  Conversely, those who are even in high position, the firstborn, can opt out of the "family of Christ" by avoiding the covenants, or failing to "endure to the end."

Husbands and wives are easily substituted in the covenant of marriage.  The “New and Everlasting Covenant of Marriage” is the highest covenant in mortality.  It links people together forever, sealing them in the family of Christ.  However, those who do not fulfill the promise are taken out of that triangle, while the faithful spouse remains.  The faithful spouse is then “given to another” who is also faithful and they automatically form a new couple in the covenant, though they never actually knelt across the altar.  Their original covenant with God continues, and the new spouse just fills in the empty space left by the unfaithful one.

The children can also be substituted.  Those children who keep the covenant can be adopted into a faithful family, becoming children of parents to whom they have no mortal connection.  Those who are "born in the covenant" are tied to their parents as long as their parents are faithful; if not, they are still sealed to Jesus Christ and can be substituted into any family with faithful parents.  Adoption is "as if" they were born to those parents.  There is no distinction, genetically.  Children can also "opt out" of a faithful family by not keeping their covenants.

Because of this, the spiritual concept of "family" is very different from the mortal "mother, father and their children" we commonly think of.  The family of the flesh is only a temporal institution that has a purpose of raising children physically to maturity.  It is temporary.  It is not by birth or genetics that a "forever family" is determined, but rather by covenants and faithfulness to them.  The only family that is "forever" is the one with a faithful man, a faithful woman, and their faithful children.  This forms a permanent "welding link" of the family of Christ throughout all the generations of the Earth.  Thus, He is the Father, as well as the Son.