Because Abram obeyed the command to be a blessing (12:2), God gave him three more promises.
those who curse you: People who ignored Abram and his covenant were rejecting God's choice and plan.
all the families on earth will be blessed: By faith, they could join the covenant God was making with Abram. The blessing spread worldwide through Abraham, Israel, the covenants, the prophets, Scripture, and the Messiah (Galatians 3:8, 16; compare Romans 9:4–5).