I have heard arguments that Gen. 12:3 applied only to Abram and not to his descendants. What is your response?
When God said “I will make you into a great nation and I will bless you; I will make your name great, and you will be a blessing. I will bless those who bless you, and whoever curses you I will curse; and all peoples on earth will be blessed through you” (Genesis 12:2-3), He was speaking to Abraham. However, these promises were later confirmed to Isaac (Gen. 26:2-4), and to Jacob (Gen. 28:13-15) where God expanded His commitment to include their descendants. He told Isaac his descendants would be as numerous as the stars in the sky, and to Jacob He promised descendants who would be like the dust of the Earth, spreading out to the west and to the east, to the north and to the south. To both He promised that all nations of the earth would be blessed because of them and their offspring.
Although the promise to “bless and curse” in Genesis 12:3 was not specifically repeated to Isaac and Jacob, most scholars believe the Lord meant for it to apply to the “great nation” He was going to build for Abraham.