Abram had only a promise from God. We see his faith in his willingness to obey God strictly in the confidence that what God had promised He would perform ( Hebrews 11:8). This divine promise was the seed from which the Abrahamic Covenant grew (ch15). The promise here included few details; it was only a general promise of descendants ( Genesis 12:2) and influence ( Genesis 12:2-3). The Hebrew text says, "be a blessing" ( Genesis 12:2), not "you shall be a blessing." This was a command rather than a prediction. However as Abram blessed others he would become a blessing (i.e, enriched, as in enriched uranium or plutonium). God would make his life more rich and powerful, and he would enrich the lives of others. [source][source][source]
"The promises that this glorious God gave to Abram fall into three categories ( Genesis 12:2-3). First there were personal promises given to Abram. God said, "I will bless you; I will make your name great." Then there were national promises given to this childless man. "I will make you into a great nation." And finally there were universal promises that were to come through Abram. "You will be a blessing ... and all peoples on earth will be blessed through you."" [1][source]
"Five times in Genesis 12:2-3 Abraham is said to be "blessed" or a "blessing" to others. This harks back to the first great blessing of mankind at creation ( Genesis 1:28) and its renewal after the flood ( Genesis 9:1). Moreover, Abraham is to become "a great nation," comparable presumably to the seventy nations listed in Genesis 10. His name will also be "great," whereas the men of Babel who tried to make themselves "a name" were frustrated ( Genesis 11:4-9)." [2][source]
Three nuances of blessing include prosperity ( Genesis 13:2; Genesis 13:5; Genesis 14:22-23; Genesis 24:35; Genesis 26:12-13; Genesis 30:43; Genesis 32:3-21), potency or fertility ( Genesis 1:28; Genesis 13:16; Genesis 15:5; Genesis 22:17; Genesis 26:4; Genesis 28:3; Genesis 28:14; Genesis 35:11) and victory ( Genesis 1:22; cf. Genesis 22:17). [source][source][source]
The Hebrew words translated "curse" in Genesis 12:3 are significant. The word qll in "the one who curses you" really means "disdains," but the word "rr in "I will curse" means "curse." It was only disdain for Abraham that would provoke God"s judgment. [source][source][source]
God"s ultimate purpose was to bless all the peoples of the earth through Abraham and his seed. [3][source]
"Any promise God gives must be appropriated by faith." [3][source]
"The remarkable thing about Abraham was his deep, unwavering faith." [5][source]
The amillennial interpretation of this promise is that it "does not pertain today to unbelieving, ethnic "Israel" (see Romans 9:6-8; Galatians 3:15) but to Jesus Christ and his church (see Genesis 12:7; Genesis 13:16 and notes; Galatians 3:16; Galatians 3:26-29; Galatians 6:16)." [6] This interpretation applies the promise to the spiritual seed of Abraham and not to the physical seed. However, there is no reason for accepting this more obscure explanation. Abraham understood the promise as applying to his physical descendants, and later revelation encourages us to understand it this way too. [source][source][source]
Revelations to the PatriarchsAbrahamIsaacJacobJoseph Genesis 12:1-3Genesis 26:2-5Genesis 28:12-15Genesis 37:5-7Genesis 12:7Genesis 26:24Genesis 31:3Genesis 37:9Genesis 13:14-17Genesis 31:11-13 Genesis 15 Genesis 32:24-29Genesis 17:1-21Genesis 35:1 Genesis 18 Genesis 35:9-12Genesis 21:12-13Genesis 46:2-4Genesis 22:1-2Genesis 22:15-18[source]