Serving Hashem without ulterior reward

מה שהבטיחו הקב"ה כל כך הבטחות נראה כי הי' להגדיל הנסיון לראות אם יהי' הליכתו בעבור השכר.

The fact that the Kadosh Baruch Hu promised him so many promises - it appears that this was in order to magnify the nisayon, to see whether his going would be for the sake of the reward.

The lavish promises made to Avraham before "Lech Lecha" were themselves part of the test: would he go in order to collect the rewards, or purely to fulfill Hashem's will?

ובאמת כתיב וילך אברם כאשר דיבר אליו ה' שלא הלך רק לעשות רצון הבורא ית':

And in truth it is written, "And Avram went as Hashem had spoken to him" - that he went solely to do the ratzon of the Creator, may He be blessed.

The Torah testifies that Avraham passed the test: he went simply because Hashem said so, not for any promised reward.

Summary: The abundant promises Hashem made to Avraham were a deliberate enlargement of his nisayon - a test of whether he would journey for the sake of reward; the pasuk "and Avram went as Hashem had spoken" testifies that he acted purely to fulfill the ratzon Hashem.