If you take the left, then I will go to the right

Genesis 13:9
 Is not the whole land before you? Please separate from me. If you take the left, then I will go to the right; or, if you go to the right, then I will go to the left.”

The context of this is that Lot and Abraham were about to split up their camps because it got too crowded and difficult to share the limited resources. Abraham, being the uncle and elder and leader, had the right to choose the land for Himself first. However, Abraham chose to forgo his right and gave his nephew Lot the first choice of land. This rather unnatural decision is perhaps an indication of God's work in Abraham as Abraham began to built his faith and trusted that God is the ultimate provider. He recognised that wise decision means using more than his own intellect, but rather trusting God to provide the best for him.

A deep sleep fell upon Abram; and behold, horror and great darkness fell upon him

Genesis 15:12
Now when the sun was going down, a deep sleep fell upon Abram; and behold, horror and great darkness fell upon him.

This event was during the time when God sealed the covenant with Abraham. Various promises had already been given to Abraham at various times. During this event, God sealed the covenant in a ceremonial fashion. God himself passed through the between the sacrificial animals while Abraham was not physically involved. Perhaps this also highlights Yshua's work at the cross, and our faith is believing in His promises. In this specific event, God reiterated the promise of land.