The Talmud states:1 "Even Daniel was answered only in the merit of Avraham." Avraham's spiritual service consisted of revealing G-dliness within the world by explaining G-dliness to even the most simple people.
The Torah tells us:2 "Avraham planted an eshel [tree] in Be'er Sheva, and called out there in the name of G-d, L-rd of the universe."
Our Sages say about this verse:3 "Do not render the verse to mean [merely] vayikra that Avraham called out. Instead, render the verse to [also] read vayakri he saw to it that the whole world proclaimed the name of G-d."
Avraham accomplished this through the eshel that he planted. Eshel is an acronym for the three words achilah, shinah, leviyah,4 "eating," "sleeping" and "escorting." After Avraham's guests would finish the food and drink he provided, they would begin to thank him. He would reply: "Was it from mine that you ate, that you are thanking me? All that you ate belongs to G-d, the Creator of the world." He would then explain the concepts of creation and Divine Providence. The guests would then proceed to praise and thank G-d.
Avraham's performance of his spiritual service with total self-sacrifice enabled him to attain the highest levels of the Blessed En Sof, the level of the "one eye of Atika Kadisha." For this reason, our Sages say that the phrase:5 "The eye of the L-rd is directed toward those who fear Him"6 refers to Avraham, for he was able to reach the supreme level of the "one eye" of Atika Kadisha.
The Midrash proves that "those who fear Him" refers to Avraham by citing the verse:7 "Now I know that you [Avraham] are a G-d-fearing man." G-d made this statement after Avraham had successfully withstood his tenth [and most severe] test. It was through Avraham's spiritual self-sacrifice and endurance that he was able to reach the loftiest of levels.
It is for this reason that regarding the binding of Yitzchok we read:8 "And he bound his son and placed him above the wood [eitzim]." "Eitz" tree or wood, alludes to the Tree of Life (the Written Torah) and the Tree of Knowledge (the Oral Torah).9 The oral Torah is likened to the Tree of Knowledge, for studying the oral Torah rectifies the sin of eating from the Tree of Knowledge.
Avraham surpassed even the rarefied levels of the Trees of Life and Knowledge and attained the level of Atika Kadisha by successfully passing the test of binding his son Yitzchok. It was necessary for Avraham to draw down the highest of levels in order to permeate even the most lowly level. This is in keeping with the well-known axiom:10 "The higher the light, the lower its ability to descend."
We observe this with regard to vision and hearing, in that the power of sight is loftier than hearing. Yet vision is limited to the observation of physical matters; compared to the objects one sees, sound is spiritual. The explanation is that since the power of sight is loftier, it is able to descend further, and perceive even physical objects.
The same is true regarding Avraham's spiritual service. In order for G-dliness to be revealed in the nether levels, it was necessary for Avraham to draw down the extremely high level of the "one eye of Atika Kadisha."
In summary: Avraham's explaining of G-dliness to even the most simple people involved a great deal of self-sacrifice. Through his spiritual service, Avraham attained a level even higher than the Trees of Life and Knowledge the Written and Oral Torah; he attained the level of the "one eye of Atika Kadisha."