Genesis 15:10

10.And divided them in the midst. That no part of this sacrifice may be without mystery, certain interpreters weary themselves in the fabrication of subtleties; but it is our business, as I have often declared, to cultivate sobriety. I confess I do not know why he was commanded to take three kinds of animals besides birds; unless it were, that by this variety itself, it was declared, that all the posterity of Abram, of whatever rank they might be, should be offered up in sacrifice, so that the whole people, and each individual, should constitute one sacrifice. There are also some things, concerning which, if any one curiously seeks the reason, I shall not be ashamed to acknowledge my ignorance, because I do not choose to wander in uncertain speculations. Moreover, this, in my opinion, is the sum of the whole: That God, in commanding the animals to be killed, shows what will be the future condition of the Church. Abram certainly wished to be assured of the promised inheritance of the land. Now he is taught that it would take its commencement from death; that is that he and his children must die before they should enjoy the dominion over the land. In commanding the slaughtered animals to be cut in parts, it is probable that he followed the ancient rite in forming covenants whether they were entering into any alliance, or were mustering an army, a practice which also passed over to the Gentiles. Now, the allies or the soldiers passed between the severed parts, that, being enclosed together within the sacrifice, they might be the more sacredly united in one body. That this method was practiced by the Jews, Jeremiah bears witness, (Jeremiah 34:18,) where he introduces God as saying, ‘They have violated my covenant, when they cut the calf in two parts, and passed between the divisions of it, as well the princes of Judas, and the nobles of Jerusalem, and the whole people of the land.’ Nevertheless, there appears to me to have been this special reason for the act referred to; that the Lord would indeed admonish the race of Abram, not only that it should be like a dead carcass, but even like one torn and dissected. For the servitude with which they were oppressed for a time, was more intolerable than simple death; yet because the sacrifice is offered to God, death itself is immediately turned into new life. And this is the reason why Abram, placing the parts of the sacrifice opposite to each other, fits them one to the other, because they were again to be gathered together from their dispersion. But how difficult is the restoration of the Church and what troubles are involved in it, is shown by the horror with which Abram was seized. We see, therefore, that two things were illustrated; namely, the hard servitude, with which the sons of Abram were to be pressed almost to laceration and destruction; and then their redemption, which was to be the signal pledge of divine adoption; and in the same mirror the general condition of the Church is represented to us, as it is the peculiar province of God to create it out of nothing, and to raise it from death.