The vision:-

The Lord answered and said: ‘Take me a cow of three years old, and a she goat of three years, and a ram of three years, a turtle also, and a pigeon. And he took all these, and divided them in the midst, and laid the two pieces one against the other; but the birds he divided not. And the fowls came upon the carcasses, and Abram drove them away. And when the sun was setting, a deep sleep fell upon Abram, and a great and darksome horror seized upon him… And when the sun was set, there arose a dark mist, and there appeared a smoking furnace and a lamp of fire passing between those divisions.

An interpretation:-

‘He did not divide the birds’ because carnal men are divided among themselves, whereas spiritual men are not divided in any way…The birds descending upon the divided carcasses do not signify anything good, but rather the spirits of this lower air, looking for their own food from the divisions of carnal men. That Abram sat by them signifies that even amidst those divisions of carnal men the truly faithful will persevere to the end. And the horror that assailed Abram around sunset, and the great and darksome fear, show that about the end of this era there will be great distress and tribulation coming on the faithful… Then follows this description: ‘Now when the sun was set, a flame appeared and behold a smoking furnace and burning torches which passed between the divided carcasses.’ For the affliction of the City of God, such an affliction as has never happened before, which is to be expected in the future under the power of Antichrist, is symbolised by Abram’s mighty and darksome fear just before sunset, that is, when the end of the world is approaching. In the same way at sunset, that is, at the very end, this fire symbolises the day of judgement as it separates the carnal men who are to be saved by fire from those who are to be condemned to punishment in the fire (St Augustine, City of God, XVI, 24).