B'resheet 15:12 Now when the sun was going down, a deep sleep fell upon Abram; and behold, terror and great darkness fell upon him.
A deep sleep - The Hebrew word tardemah (tar-day-maw'); a lethargy or (by implication) trance:
(Biblesoft's New Exhaustive Strong's Numbers and Concordance with Expanded Greek-Hebrew Dictionary. Copyright (c) 1994, Biblesoft and International Bible Translators, Inc.)
G-d put Abram into a deep sleep. This may seem odd, because NORMALLY Abram should have been awake to participate in the covenant. However, the contract was not contingent upon anything that Abram would need to do. It was totally G-d who was responsible for the terms of the contract.
This is also symbolic. The deep sleep that Abram experiences represents our sinful state of being dead to sin. Just as Abram was unable to wake himself up and participate in the terms of the covenant, we are powerless in our sinful condition and unable to do anything to save ourselves.
Terror and great darkness - This symbolizes the awfulness of the sin that each of us carries until we ask the L-rd to forgive us of our sin and accept Yeshua's shed blood as eternal payment for our sins.
B'resheet 15:13-16 And G-d said to Abram, "Know for certain that your descendants will be strangers in a land that is not theirs, where they will be enslaved and oppressed four hundred years. But I will also judge the nation whom they will serve; and afterward they will come out with many possessions. And as for you, you shall go to your fathers in peace; you shall be buried at a good old age. Then in the fourth generation they shall return here, for the iniquity of the Amorite is not yet complete."
This is prophecy that has already come to pass. The children of Israel were in Egypt for over 400 years.
Sh'mot (Exodus) 12:40-41 Now the time that the sons of Israel lived in Egypt was four hundred and thirty years. And it came about at the end of four hundred and thirty years, to the very day, that all the hosts of the L-RD went out from the land of Egypt.
B'resheet 15:17 And it came about when the sun had set, that it was very dark, and behold, there appeared a smoking oven and a flaming torch which passed between these pieces.
The Fifteenth letter corresponding to this chapter is Samech - Divine presence and support; stands for the Holy of Holies of the Temple.
Ruach HaKodesh walked through the halves. This is appropriate in regard to the 15th letter of the Hebrew alphabet since Ruach HaKodesh is Divine. Ruach HaKodesh also dwelt in the Holy of Holies in the temple. G-d was the one who would have to keep the promise regardless of Abrams actions. Abram did not walk through the halves.
It is the same with us we are powerless to atone for our own sins eternally. No mitzvah no matter how great can do it for us. Ha Shem knew that was the case so he made a plan to save us. We accept his plan that same way Abram did by FAITH. Abram only had to believe G-d and trust His word that he would have an heir and he would inherit and "cross-over" into the Promised Land. We also must trust in His word that we will inherit and one day "cross-over" into the heavenly Promised Land. We do that by accepting Yeshua as our Mashiach and His death on the execution stake as atonement for our sins.
Through the spiritual implications of this covenant, when we have faith in Yeshua we are promised the indwelling of the Spirit in our temples permanently.
Romans 4:13 For the promise to Abraham or to his descendants that he would be heir of the world was not through the law, but through the righteousness of faith.
Galatians 3:13-14 But Messiah (Christ) has bought us out from under the doom of that imperfect system by taking the curse for our wrongdoing upon himself. For it is written in the Scripture, "Anyone who is hanged on a tree is cursed" [as Yeshua (Jesus) was hung upon a wooden stake] that the blessings of Abraham might come on the Gentiles through Yeshua Messiah; that we might receive the promise of the Spirit through faith. KJV
B'resheet 15:18-20 On that day the L-RD made a covenant with Abram, saying, "To your descendants (Physical) I have given this land, From the river of Egypt as far as the great river, the river Euphrates: the Kenite and the Kenizzite and the Kadmonite and the Hittite and the Perizzite and the Rephaim and the Amorite and the Canaanite and the Girgashite and the Jebusite. " NAS
Here is the boundary I was referring too earlier. Notice, all the way to the river Euphrates. The entire area promised to Abram will probably not be under Israeli control until the true Messiah comes and sets up his throne.