Parashat Lekh-Lekha begins with God’s initial revelation to Avraham, in which He commanded the patriarch to leave his homeland and relocate (12:1), and promised to bless him (12:2-3). In the next verse, we read, “Avram went as God had told him…” (12:4).
Rav Shimshon Refael Hirsch, in his commentary (see also Malbim), notes the shift in the Torah’s terminology between the first and fourth verses in this parasha. In the first verse, the Torah employs the term va-yomer (“said”), whereas the fourth verse records that Avraham left his homeland as God had “told” him – diber. Quite often, the verb d.b.r. is used in reference to instruction and commands, as opposed to simply relating information. Rav Hirsch thus explains that in the first verse, when the Torah introduces God’s statement to Avraham, it employs the more generic term va-yomer, since it incorporated both a command and a promise. But in describing Avraham’s response, the Torah writes that he left “ka’asher diber elav Hashem” – as “God had told,” or commanded. As Rav Hirsch comments, “…Abraham did not obey the promise but the order of God. He went because God had told him to.” His primary motivation in leaving his homeland and relocating in Canaan was the divine command, the fact that he was ordered to do so. It was the command, not the promise of reward and success, that drove him to act. According to Rav Hirsch, then, this verse teaches us to perform mitzvot out of a sincere desire to fulfill the divine will, and not simply for the purpose of earning reward.
The Netziv, in his Ha’amek Davar, presents a different reading of this verse (one which does not explain the transition from va-yomer to diber). In his view, the words “ka’asher diber” (“as [the Lord] had told”) actually means, “when [the Lord] had told.” According to the Netziv, the Torah here emphasizes that Avraham left immediately upon hearing God’s command, without delay. Rather than delaying his journey until he completed his preparations and the sale of his property and possessions, Avraham immediately embarked on his trip, leaving behind his wife and servants to complete the preparations and sales. Avraham’s response is thus intended to set an example of zeal and alacrity in performing mitzvot, the importance of fulfilling our duties swiftly and responsibly, rather than delaying them in favor of other, less critical matters.