Genesis 15:10

(Verses 10, 11.) And he placed them opposite each other: but he did not separate the birds. However, birds descended upon the carcasses and the divisions thereof, and Abram drove them away. It does not pertain to the present work to explain the sacrament. We only say this, because the Hebrew version has for these words: And birds descended upon the carcasses, and Abram drove them away. For he deservedly often delivered Israel from narrow straits.

And it is said, "But the birds divided he not," because carnal people are divided among themselves. But those who are spiritual are not divided at all, whether they seclude themselves from the busy conversation of humankind, like the turtledove, or dwell among them, like the pigeon. For both birds are simple and harmless, signifying that even in the Israelite people, to which that land was to be given, there would be individuals who were children of the promise and heirs of the kingdom that is to remain in eternal felicity.

Now notice carefully Abraham is said to have divided the three animals into two parts and to have placed them one against the other. "The birds," says Scripture, "he did not cut in two." Why is this, brothers? Because in the church catholic, carnal people are divided but spiritual people are not. And, as Scripture says, they are separated one against the other. Why are carnal people divided and set against each other? Because all wicked lovers of the world do not cease to have divisions and scandals among each other. For this reason they are divided, since they are opposed to one another. However, the birds, that is, spiritual souls, are not divided. Why not? Because they have "one heart and one soul in the Lord." To will and not to will is all one thing to them. Surely the turtledoves and pigeons that we mentioned above are like these souls. In the turtledove chastity is represented, and in the pigeon, simplicity. All God-fearing people in the church catholic clearly are chaste and simple, and with the psalmist they can say, "Had I but wings like a dove, I would fly away and be at rest." And again: "The swallow finds a nest in which she puts her young." Carnal people, who can be divided, are pressed down by the heavy fetters of vice. Spiritual people are raised on high by the wings of various virtues. As if by two wings, that is, the two precepts of love of God and charity toward the neighbor, they are lifted up to heaven. With the apostle they can say, "But our citizenship is in heaven." As often as the priest says, "Lift up your hearts," they can say with assurance and devotion that they have lifted them up to the Lord. However, very few and rare are the people in the church who can say this with confidence and truth. Therefore Abraham did not divide the birds, because spiritual souls who have one heart and soul, as I said, cannot be divided or separated from love of God and of neighbor. They exclaim with the apostle, "Who shall separate us from the love of Christ? Shall tribulation, or distress or persecution?" Other words follow until it is said, "Nor any other creature will be able to separate us from the love of God, which is in Christ Jesus our Lord." Therefore spiritual souls are not separated from Christ by torments. Carnal souls are sometimes separated by idle gossip. The cruel sword cannot separate the former, but carnal affections can remove…