What is the seed?
The seed are potential sons of God. I say potential because they are not sons until they are fertilized (by holy spirit) and thus "conceived." They are the "eggs" of the Woman (the spirit realm, "Sarah"... aka "Jerusalem ABOVE")... which eggs can be "fathered" by God... or by another ("You are from YOUR father, the Devil"; "Another man sowed HIS seed"). As spirit beings, they differ from angels in that angels are not sons but SERVANTS of the "household" (they are not born by holy spirit but were created "as is") will never be sons.
When the seed of the Woman (spirit realm) is fertilized by the seed of God (holy spirit), a new "creation" results: an zygote/embryonic "being"... awaiting birth. That "birth" occurs when such ones put OFF flesh (the unclean robe/soiled OUTER garment that is "unclean" because... by means of the BLOOD in it... human hemoglobin, etc., it has sin and death IN it - it is CORRUPTIBLE... which is what makes it MORTAL. Not sin of commission of error, but sin that is sickness, aging, and death)... and put ON a spirit body (the "white robe/clean OUTER garment, "clean" because... by means of the BLOOD in it... God's blood, holy spirit... it has NO sin or death in it - it is INcorruptible... which is how it becomes IMmortal).
Although many profess to be "born again" NOW, that is actually not the literal case. Some have a received a TOKEN of that birth... the anointing with such holy spirit... so that they can say they are [as good as] born again; however, the actual BIRTH... occurs when they are either resurrected to such incorruptible body... or changed to it (those who die are brought back to life; those who have not died are changed, and so never die). This has not occurred yet (although, both Elijah and Moses have already been changed, and Christ resurrected to life, the only one to not die AGAIN).
Why is it necessary?
To understand that, you have to understand why the whole thing came into existence in the FIRST place (not just the physical realm, but ALL of it, starting with Christ). Christ is the Son... of God's LOVE. LOVE is what prompted the Most Holy One of Israel to bring a son into existence. NOT loneliness, as some falsely teach - . He could have just created angels to remedy that. But He loved the spirit realm (Sarah; Jerusalem Above) SO much... it prompted an act of love, which act resulted in the "birth" of His Son, the HOLY One of Israel. Then, using that Son, He created servants for them... NOT chained, oppressed servants, but beings that could... and would... willingly do what they wanted/needed to have done.
Because of the love and loyalty of this Son, God decided there would be more. It became evident, however, that some of those servants, having been misled by another, which wouldn't be last time)... began to have their own ambitions: to destroy the Son and usurp his inheritance. Their ambitions included destruction of the rest of the seed, as well, because even if they managed to get the firstborn, they would still have to deal with the others (who would also inherit, as sons).
To protect the seed, the Son became a "propitiatory"... or "covering" for the "place" where the seed resided: the "ark" of the Woman. In her womb, per se. To protect the SON... two spirit beings (cherubs) were given to HIM. They are/were the angels OF the ark... or the "arkangels." They were given positions "upon" the Cover... with their faces to always be "toward" him. One cherub was and is Michael; the other is Belijah'el (Belial)... whom you may refer to as "Satan" and/or "Devil." Michael remained... and has still remained... loyal. To God, to the Cover (Christ)... and to the seed in the ark. That is why he is referred to as the "Prince of you people" (Note: a "prince" is not the son of king in the spirit realm - a prince is simply one placed over a "principality" or territory). The other, the "Prince of Persia" (because Persia, including Eden and the garden in it... was HIS principality), not only betrayed the Cover... but the contents of the ark: the seed (of the Woman).
The "law" that regulates protection of the seed was and is called a "Law Covenant" (which is why you have the Ark... of the COVENANT). So long as the seed adhere to the Law... the God is BOUND to protect them from their enemies... including Death (the greatest and last enemy!). Thus, Abel, Enoch, Noah, Abraham, Lot, Isaac, Jacob, etc. Starting with some of Jacob's (Israel's) sons, however, the Law began to fade from the heart.
Skip past Israel's residency in Egypt (a lot to explain there and I'm trying to keep this as simple as I can)... to the point where the offspring of Abraham et al. find themselves in the wilderness of Sinai... showing again and again that the "Law" is NOT written on their hearts (where it SHOULD have been, by means of holy spirit; however, they kept rejecting that spirit... through their lack of faith, murmuring, disloyalty, and treatment of their fellowman, etc.). So, the Law was written (Note: NOT the behemoth of "law" that is canonized in the Bible - those are additions by Moses, who had permission to do so as Israel kept rejecting the "10" - he had to break it down... and down... and down... and down... because they just WOULD not "get" the purpose of the "10" - to love one's neighbor AS oneself).
Skip to Christ coming in the flesh. To (1) bear witness to the truth (about God and the Law); (2) demonstrate how to LIVE the Law... versus pointing the finger at and worrying about everyone else; (3) give his life... so that his blood could be poured out to atone for the sins of ANYONE who wanted to take advantage of that "gift"; and (4) present himself as a sacrifice FOR those who so took advantage, in order to open the way into the spirit realm for THEM... by means of giving them GOD'S blood, holy spirit... as well as, in the future, spirit bodies that will allow them to literally enter (actually, re-enter, but now as full grown sons). In doing all of this, he instituted a NEW "law"... with love being the ONLY feature... and "covenanted" to shield from Death those who accept and live by that agreement. He knew they would fall short, of course, as Israel did; however, so long as they put faith in HIM AND HIS BLOOD (holy spirit, which "washes" one "clean" and so "blots out" such errors)... one can still look foward to life (everlasting in the kingdom of God).
Thus, such ones, by means of eating and drinking the flesh and blood of Christ, literally "ratify" their agreement to the Covenant and so, once again, are as good as in the "Ark" (of the Covenant)... where they are protected (from the "last enemy," Death)... until they can be BORN (again, and this time as the spirit beings they actually are... on the INSIDE).
Of course, I've left out a lot of details, but more and your head may spin even more, so I'll stop here and let you chew on this "summary" of sorts.
I get that it sounds "mythical" and like a fairy tale/ancient fable, etc., dear one. I am not so... ummmmm... gullible that I believe in mythology. I know this to be true, though, because of the One who explained it to ME. He is real. He is alive. No, he is not physically embodied (nor was he to start), and for some that's just too sensational to grasp. I get that. But I would be absolutely LYING to you... if I denied what I've been told... and seen (and, yes, I have seen some of this - it was how I came to understand a lot that I do)... as well as the One who told me and showed me. So, you don't have to believe me; that really is not my concern. I am much more concerned with disappointing him... than I am with disappointing anyone here. I have learned that he can save me from death (of the SPIRIT, which only sleeps); no one here can do that, so...
So, I hope this helps, dear Jay88. Please let me know if you need further explanation and I will try to share what I can. Again, peace to you!
YOUR servant and a slave of Christ,