At Aish.com is an article titled Abraham’s Discovery (http://www.aish.com/tp/i/moha/48909077.html), in which it says:
And God said to Abram: ‘Go out from your country, from your birthplace, from the home of your father, to the land which I will show you …’ [Genesis 12:1]
This Torah portion begins with the Divine directive to Abram (later to be known as Abraham) to leave his home for a destination unknown.
Who was this man Abram and why was he chosen for this special directive? How had he merited God’s attention? Why was he, of all people, destined to become the first of the patriarchs, the father of many nations?
Regarding all these questions, the Torah is silent.
Of course, the Midrashic literature ably fills in all the gaps, recounting Abram’s many trials and tribulations as a child and young man. We are told of his lonely spiritual quest and eventual discovery of the One God. While we have no question about the authenticity of the Oral Tradition, why does the Torah itself not share these details with us?
Of course, such a question could be posed about any section of Midrash, but, in this instance the complete lack of explanation of Abram’s special status in the Torah leaves us especially puzzled.
The article goes on to note that Abr(ah)am got metaphysical inspiration about ultimate origins from observing that his brother, Nahor, was named after their father’s father.
The article seems to imply that this was the source of Abr(ah)am’s initial metaphysical inspiration. Perhaps it was, but the seed which sprouted into becoming that inspiration was planted at some point prior to that actual inspiration, likely in Abr(ah)am’s childhood. As even a Roman Catholic source (http://www.scborromeo.org/papers/melchizedek.pdf) points out about the long lives within the geneology of Abr(ah)am:
the sacred author…wants us to be able to see the connection between Shem/Melchizedek and Abraham; otherwise this genealogy which gives all these [long] ages would not have been included.
No revelation is recored as having been given to Shem, and his name is not expressly connected to the name ‘Melchizedek’. The reason the Torah is silent about where Abr(ah)am got his inspiration is because Abr(ah)am was to be the father of a new world order, just as Adam had been the father of the old. This meant that Shem was more onlooker than participant, seed-planter than waterer, tiller than protector-guide, in Abr(ah)am’s story. The main thing Shem did was to bless Abr(ah)am, and he did this while having entirely down-played his own role in it, by having it recorded that Abr(ah)am was blessed by a title: Melchizedek. In other words, Shem was a humble man, not only despite his god-like long life relative to those then living, but in light of his own somber sense at how feeble was the one he blessed.
To Shem, his own long life was a trivial fact. But, he knew that its express connection to Abr(ah)am could only end up becoming a greedily worshipped legend—the sort of greedy worship which he knew could only take limelight from the role which Shem’s title must play for Abr(ah)am’s own, far greater, story. The title, and its connection to the life-span of its owner relative to Abr(ah)am’s own short duration, was that role.