The Seed of Abraham - the people of God whom He foreknew

[telnetd]

In Romans 11:1–2 Paul outlined God’s relationship with the seed of Abraham. What did 
Paul mean when he said that God “foreknew” His people? Paul also indicated that some 
people were chosen in Christ “before the foundation of the world” (Ephesians 1:4). 
This statement suggests that many were called in the premortal world and chosen to 
receive special blessings contingent upon their faithfulness. These special blessings 
assume at least two dimensions.

First, wrote Elder McConkie, “this election to a chosen lineage is based on pre-
existent worthiness and is thus made ‘according to the foreknowledge of God.’ (1 Pet. 
1:2.)” Elder McConkie explained that “to bring to pass the salvation of the greatest 
possible number of his spirit children the Lord, in general, sends the most righteous 
and worthy spirits to earth through the lineage of Abraham and Jacob. This course is 
a manifestation of his grace or in other words his love, mercy, and condescension 
toward his children.” (Mormon Doctrine, p. 216.) Thus, those born into the lineage of 
Abraham, Isaac, and Jacob have through the centuries heard the testimony of prophets, 
had access to the sacred scriptures and ordinances, and been at the forefront of the 
work of God upon the earth. (See Harold B. Lee, in Conference Report, Oct. 1973, pp. 
7–8; or Ensign, Jan. 1974, p. 5.)

Second, “as part of this election, Abraham and others of the noble and great spirits 
were chosen before they were born for the particular missions assigned them in this 
life” (McConkie, Mormon Doctrine, p. 216). Doctrine and Covenants 138:56 indicates 
that the noble and great ones “received their first lessons in the world of spirits 
and were prepared to come forth in the due time of the Lord … for the salvation of 
the souls of men” (see also Abraham 3:22–23; Jeremiah 1:4–5).
(Religion 430 and 431 - Doctrines of the Gospel Student Manual, chapter 19).

Are the seed of Cain considered part of this "seed of Abraham", whom are classified as God's
people whom He foreknew?

[The Nehor]

The people in Romans 11:2 that God foreknew are Israel or the Jews. It was not intended to refer to any form of preexistent or premortal state.

[Pyreaux]

Based on both biblical chronology and Latter-day Saint theology, the short answer is no. Cain and Abraham belong to completely different lines and eras. Cain was the firstborn son of Adam, while Abraham is a direct descendant of Seth. Therefore, anyone tracking Eve's promised lineage is looking at an entirely separate branch of the human family tree than the lineage of Cain.

In a sense, God the Father "foreknew" every spirit before they came to earth. He chose a lineage to carry the priesthood, the scriptures, and the gospel ordinances to the rest of the world and the firstborn as a savior would be born in the exact time and circumstance. The Jewish premortal existence was the Guf has much in common with Latter-day Saint concepts of the premortal existence than it does with Calvinist predestination. A pre-existing storehouse or community of conscious spirits waiting in a specific order for their turn on Earth. 

Wisdom of Solomon 8:19–20, Solomon explicitly describes himself as having a good, noble soul before he was ever given a physical body, "As a child I was naturally gifted, and a good soul fell to my lot; or rather, being good, I entered an undefiled body."

Notice the order of operations, "being good, I entered..." Solomon is explicitly stating that his spirit, his "goodness," was already developed before he descended. He did not start as a blank slate at birth; his spirit already possessed individual identity and nobility that entered the noble body, his "undefiled" house.

LDS doctrine teaches the premortal life, individuals developed there and some were foreordained (appointed or set apart based on their faithfulness) to fulfill specific missions or roles during their mortal lives. Not destined to fulfilled, per se.

In both traditions, your soul did not pop into existence out of nothingness at the moment of your physical conception. You existed somewhere specific in the heavenly realm, waiting for a physical body.

LDS theology also emphasizes that lineage is not a guarantee of salvation, neither is it a barrier. According to teachings from Joseph Smith and subsequent church leaders, anyone of any lineage who accepts the gospel of Jesus Christ and receives the proper ordinances is spiritually adopted into the seed of Abraham.

"For as many of you as have been baptized into Christ have put on Christ... And if ye be Christ’s, then are ye Abraham’s seed, and heirs according to the promise." (Galatians 3:27, 29)

Edited 3 hours ago by Pyreaux

[telnetd]

1 hour ago, Pyreaux said:

In a sense, God the Father "foreknew" every spirit before they came to earth. He chose a lineage to carry the priesthood, the scriptures

What lineage and what priesthood?