Commentaire sur La Genèse 12:7

ויבן שם מזבח AND HE BUILDED THERE AN ALTAR — in thanksgiving for the good tidings that he would have children, and for the good tidings that they would possess the land of Israel.

The sense of the expression, And there he built an altar unto the Eternal, who appeared unto him,⁵⁷Verse 7 here. is that he gave praise to the Glorious Name⁵⁸Deuteronomy 28:58. and offered unto Him a sacrifice of thanksgiving for His having appeared to him. Until now G-d had not appeared to him neither in a mar’eh nor in a machzeh.⁵⁹Mar’eh and Machzeh are terms for different degrees of prophetic vision. See Ramban further, 15:1. See also Moreh Nebuchim, II, 41-5, for full discussion of these terms and other prophetic experiences. Rather, the command, Get thee out of thy country, was said to him in a nocturnal dream or through Ruach Hakodesh.⁶⁰Literally, “The Holy Spirit.” See ibid., Chapter 45, beginning: “second degree of prophecy.” It is possible that the expression, Who appeared unto him, alludes to the mystery of the sacrifice. The one enlightened [in the mysteries of the Torah] will understand.

There he built an altar. God did not appear to Avraham when He gave him the order to go to Canaan because He does not grant visions outside of the Holy Land. Similarly, Avraham did not wish to build an altar where God does not allow His Presence to dwell.