Theory on Melchizedek
When looking at creation, God made the Heavens & Earth. (heavens listed first) There is nothing to suggest he did not create his heavenly family first (angles etc..)
Earth- The power(spirit) of God was moving over the water, by God's commands (words) the earth was created. We have here so far God+Spirit+word, by this all things were created, put into their rightful place and balanced to serve their purpose.
At The creation of man we have God - created man - given breath of live to become a living Soul. God + Spirit = living being + words of god to balance mankind. We see Mankind was created in the likeness of God. Eve was created in the likeness of God but also from Adam's rib (god + Adams rib + breath of life = Living being + Gods word), to create a balance in mankind. When sin entered at the garden, this caused an unbalance in Gods creation of Man.
Cain and Abel are born but not mentioned in Adams Geneaology, although the bible says Adam & Eve had intercourse, and Eve had Cain & Abel. We can see here Adam (son of God)= mankind, Eve = the mother of all living human beings, were to unite as one. In this way the both sinned in the garden and were sent out.
Cain = Farmer, Able = Shepherd. This represents the punishment to come upon mankind. Cain represented the punishment mankind would endure upon the earth. Able represented the Shepherd = a way back to God. Although the bible doesn't tell us much about what did occur in the garden, I can see here Able may have been the way back to righteousness, but as we see in scripture Shepherds are killed, as was Abel.
Seth being the next born was a replacement for Abel, who Cain (Sin) killed. With Shem, Gods NAME was then used in worship.
Another note: God says there is to be a witness to mankind. He had witnesses to his creations, and gave witnesses to man. Jesus (yahushua) I believe was created by God, God + Gods Spirit conceived into Mary = perfect uncorrupted living spirit and word of god = Son of god created in flesh, who would be a witness for God himself.
Similiar to Adams creation, but at the time of Adams creation until the fall we do not hear of flesh.
So with Melchizedek, if we believe as I do, Israel may be where the Garden of Eden was, and Adam was sent east of Eden after the fall, not able to return. \
Some years later we have Abraham being instructed to return to the promised land (a promise to return to the kingdom of God), where he meets Melchizedek (a witness to the promised land).
It is easy to understand that Melchizedek would have been a priest as a spirit of God who took on a fleshly body to confirm to Abraham he has entered the promised land, and being God's witness to the promise given to Abraham by God.
This could have also been Shem as the bible does not speak of the righteous people apart from their genealogy. In the book of Jasher, Terah was sinful and Abraham wanted to Know the one god, for some time Abraham was taught by Noah and Shem, prior to Abraham's encounter with God.
God spoke through his prophets, So for Melchizedek being a High priest (spirit of Jesus) of the god most high + King of Salem (the Priest of god, the one who brings worship of god and instruction) (the King of Salem = the promised land + entry to Gods Kingdom) Abraham received the seal of the promise.
Jesus (yahushua)conceived through Mary as the fleshly son of son had already been given this kingdom to be priest and king of for ever. His birth was to bring Gods word and truth to mankind (being born of flesh he was given a human name) but he was declared by God to be the king and Priest of Israel. Had Jesus not been born, no one would have survived as corruption had spread all over the world again.
The righteous line from what I can pick up from the bible was when the 12 tribes of Israel died during their time in Egypt, their descendants were to stay true to the teaching given to them to enter the promised land.
We see Moses did his best to restore the teaching when they came out of Egypt, and we see the decline after entering the promised land until Jesus came to begin the process of restoring all things, all the righteous from Seth through Isaac's children, would have ended and been lost for ever, & their descendants would never have received the promise given to Abraham, Issac, Jacob; Jesus (Yahushua)