פּירוש אויף בראשית 12:2

ואעשך לגוי גדול AND I WILL MAKE OF THEE A GREAT NATION —Since travelling is the cause of three things—it decreases (breaks up) family life, it reduces one’s wealth and lessens one’s renown, he therefore needed these three blessings: that God should promise him children, wealth and a great name (Genesis Rabbah 39:11).

ואעשך לגוי גדול, “I am going to make you into a great nation, etc.” G-d, being aware that Avram’s wife is presently barren, tells him that notwithstanding this fact he will become the founding father of a great nation. We had been told in Genesis 11,30, of Sarah’s inability to have children. A different interpretation of this verse: The Torah does not write: ואשימך לגוי גדול, “I will make you to be a great nation, which could have been misinterpreted.” G-d stressed that He would perform an act that would neutralise any negative decree from which Avram suffered, i.e. changing both his and his wife’s name. People called: Avraham, and: Sarah, had never been decreed to remain childless. According to the Midrash, originally Avram lacked 5 important organs: eyes, ears, as well as the glans. The glans is called “the head of the body,” as sacrificing, i.e. circumcising it is equivalent to offering one’s entire body as an offering to G-d. (Compare Talmud, Nedarim 32.) When G-d added the letter ה to his name, He supplied these missing 5 organs of his body. This is meant when G-d invited him to become תמים, “whole, a perfect specimen. (Genesis 17,1)

ואברכך, “I shall bless you;” I personally, not through any agent of mine.