Ve'e'escha legoy-gadol - I will make you into a great nation

Our Sages (Bereishit Rabbah 39:15) explain that being a traveler, a nomad, brings in its wake three negative phenomena, it results:

1. in a decrease of one's fertility
2. a decrease of one's financial resources
3. in a decrease of one's standing amongst one's peers.

G-d promised Avraham that he would not suffer from these negative phenomena.  By saying: "I will make you into a great nations," G-d told Avraham that his ability to procreate would not only not suffer but would be enhanced.  By adding: "I will bless you," G=d hinted that Avraham would prosper financially.  By further adding "I will make your name great," He countered Avraham's concern that his standing amongst his peers would decline due to his becoming a nomad.

Note that G-d did not use the customary expression, "I will let you become a great nation," but He said "I will make you into a great nation."  This is equivalent to G-d saying:  "I will make you into an entirely new phenomenon."   The expression G-d used is comparable to when the Torah said, "G-d made the sky." (1:7)

The sod of the words legoy gadol, "to a great nation," is a reference to the Jewish nation which is described in Devarim 4:8 as, "and who else is a great nation which has righteous decrees and ordinances?"  The words, "I will make you into a great nation," are alluded to when we refer to G-d as the G-d of Avraham," the words "I will bless you," are alluded to when we refer to G-d as "the G-d of Yitzchak;" the words "and I will make your name great," are alluded to when we speak of G-d as "the G-d of Yaakov."  The words "and be a blessing," prompted our Sages when they formulated the first benediction in the principal Amidah prayer to conclude with reference to Avraham only when we say Magen Avraham (the Shield of Avraham) at the conclusion of that benediction.