And I will make my covenant between me and thee, and will multiply thee exceedingly."
God had already made an internal spiritual Covenant with Abram. This Covenant that God is about to make with Abram is an external Covenant or mark of the internal Covenant. As a mark of this external Covenant that reflects the internal Covenant, God repeats the promises of the original Covenant.
And Abram fell on his face:
Abram did not accidentally trip and fall on his face (obviously). But Abram's spirit was broken and humble before God as he gave reverence and proper respect to the Lord by bowing before Him. How many Christians today (who are not handicapped and or do not have knee problems) bow before Him today?
and God talked with him, saying,
"As for me, behold, my covenant is with thee, and thou shalt be a father of many nations.
Whenever God repeats his promises to us, it is a good idea that we stop and really listen to Him. Abram had a little trouble in listening to God because He decided to have a child by means of trusting in the flesh and not in trusting in God.