The story continues with Abraham asking God how he can be sure that will be true. What follows is a strange story upon a cursory reading. Abraham was to cut up some animals and lay them out and wait. Abraham waited all day long in the hot son and chased away carrion birds. After sunset, Abraham fell asleep and God spoke again, prophesying what we now know as the time of Egyptian slavery. Then Abraham saw in a vision a smoking pot and a torch passing through the animals. Seems sort of gruesome and strange. But if we can understand what is really happening here, it makes sense and shows what is really at stake here.
After some research, I found that in the ancient Middle Eastern culture, when two people(s) entered into a covenant/promise/treaty, they would perform what was known as the 'cutting of a covenant' or Blood Path. Those taking part in the ceremony, those that are making the covenant or treaty, would take some animals and cut them apart and arrange them is such away the blood flowed to form a path in between the pieces. Then to make the covenant a legal and binding, both parties making the agreement would walk through the cut apart animals down the path of blood, signifying that they agree to the terms. They also agreed that if they did not fulfill their part of the agreement, then the animals represented what would happen. They were in reality saying "May it be done to me, like what happened to these animals, if I do not fulfill the terms of this covenant." That my friend is serious business. To agree to be ripped apart if they broke the Promise Covenant/Treaty, was a sign of the seriousness of the ceremony.
But if you notice, In Genesis 15, Abraham did not pass through the blood path. In this case it was God who was signifying it was on His part to keep the promise, and Abraham had no part in the terms being fulfilled. Not only that, God passed through as a smoking fire pot and a blazing torch (the meaning of these are not agreed upon in my research). So in a sense God passed through the blood path two times, meaning He is doubly serious about the Covenant. He was saying, like the people of Abraham's day that performed this ceremony, that may He be ripped apart if He does not fulfill His part. He was also demonstrating that when He makes a promise, or covenant, then we can be sure He will do it. In this case Abraham had nothing to fulfill, only God had His part to fulfill. (There is also reference to this ceremony in Jeremiah 34:18: "Because you have broken the terms of our covenant, I will cut you apart just as you cut apart the calf when you walked between its halves to solemnize your vows.")
What else can we learn from this passage? God knows what makes sense to us when He tells us or shows us things and puts them in terms that we recognize. If Abraham was alive today, the treaty would have the same terms, but may be played out in a way that makes sense in the culture he lives in. For example, in the USA, they may have the promise/treaty notarized, or go before a lawyer or judge to have the promise legal and binding. That is a something we can understand in our culture. It's not that God is in the business of being gruesome, but He is in the business of speaking to us in a way that we can understand.
One thing we can count on, if God promises us something, He will follow through. It may not be like we picture it or expect, but the end result will be exactly as God said it would be. It may not happen in the time we want it to, but you can be sure that God will do it in His timing, not necessarily ours. God takes His promises seriously; He will do what He says He will do. Our word and promises may fail, but God's never will.