Our Parsha opens with a colossal vacuum, a bewildering omission. God speaks to the elderly Avraham (he is 75 years old) commanding him to follow him to a new undesignated land in order to found a new nation. But we know nothing of his personal past. We all want to know: Why Abraham? What make Abraham "The One?" How did he gain this unique position in History? What act made him worthy, what virtue made him the chosen one? And why does the Torah deny us this information? Of all the personalities in the Torah, we generally receive some background to their persona. With Avraham we have a total blackout. If his history is so important, so exciting and rich, then why are we denied this history?
"Abraham, the great knight of faith, according to tradition searched and discovered God in the star-lit heavens of Mesopotamia. Yet, he felt an intense loneliness and could not find solace in the silent companionship of God whose image was reflected in the boundless stretches of the cosmos. Only when he met God on earth as Father, Brother and Friend – not only on the uncharted astral routes – did he feel redeemed. Our sages said that before Abraham appeared majestas dei was reflected only by the distant heavens and it was a mute nature which "spoke" of the glory of God. It was Abraham who "crowned" Him as the God of the earth i.e. the God of men." (Lonely Man of Faith –Tradition edition pg.32)
In this wonderful piece by Rav Soloveitchik, we read of two dimensions of the God-man experience. One can perceive of God in intellectual terms. That gives you a certain perception of God, but it is distant and impersonal. Rav Soloveitchik talks of the "Covenantal man of faith" as "craving for a personal and intimate relation with God." There is a dimension of the man-God interaction that rests in the realm of experience, not cognition, of two-way relationship, rather than independent contemplation and thought. In Parashat Lech Lecha Abraham shares an intimate relationship with God, as we see God's care and worry for Avraham as he listens to Avraham's worries and concerns and reassures him with a gentle: "Do not fear Avram, I will protect you." Where in our parsha Avraham is told, "Walk before me in perfection and I will make a covenant between Myself and you." Avraham and God from the first moment of "Lech Lecha" walk together! It is a living breathing interactive relationship with God.
When does God emerge from the shadows? At what moment does God begin to build this mode of relationship with Avraham? I would think that it is the moment that God actually addresses Avraham, when Avraham begins to act together with God, responding to His call, interacting with Him. In this perspective then, the command of "Lech Lecha" is THE watershed moment in which God transformed from being distant to close, from anonymity to familiarity. It is the critical beginning of the relationship. That moment of "Lech Lecha" is the start of the living experience of God.
For Rav Soloveitchik we are uninterested in the story prior to the great moment of God's revelation to Avraham. Why transcribe the perception of the anonymous remote distant God? We begin Abraham's history at the moment that he experiences the true God relationship; the intimacy of God. That is the beginning of the story.
READ the entire shiur here
 15:1 and see also in 13:14 where God would appear to come to reassure Avraahm and console him "after Lot departed from him."