And the Lord spoke to Moses, saying: Speak to the sons of Israel, and take from them a rod according to the houses of their families from all their princes, twelve rods; and write the name of each of them upon his own rod. And the name of Aaron write upon the rod of Levi; for there is one rod for the tribe: according to the houses of their families they shall give them to you. And you shall place them in the tabernacle of testimony over against the ark, from which I shall be made known to you there. And it shall be that the man whom I shall choose, his rod shall sprout: and I shall take away from you the murmuring of the sons of Israel, in whatever things they murmur against you. Every prince of a tribe and of a people has a rod; for one cannot rule a people unless he has a rod. Whence also Paul the Apostle, because he was a prince of the people, therefore said: "What will you? Shall I come to you with a rod, or in charity and the spirit of meekness?" All the princes of the tribes, then, must needs have their rods, but there is one alone, as the Scripture relates, the high priest Aaron, whose rod sprouted. But since, as we have often shown, the true high priest is Christ, he alone is the one whose rod of the cross not only sprouted, but also flowered and brought forth all these fruits of the believing peoples. And what is this fruit which it brought forth? "Nuts," it says — a fruit which in its first covering is bitter, in the next is guarded and covered over, and in the third feeds and nourishes the one who takes it. Such, therefore, in the audience-hall of Christ, is the teaching of the law and the prophets: the first face of the letter is bitter enough, which enjoins the circumcision of the flesh, which commands concerning sacrifices and the rest of the things that are designated by the letter that kills. All these things cast away like the bitter husk of the nut. In the second place you will come to the defenses of the shell, in which either moral teaching or the principle of continence is designated. These indeed are necessary for the guarding of those things which are kept within, yet they must at some point be broken and without doubt dissolved. As if, for example, we should say: abstinence from foods and the chastisement of the body, so long as we are in this corruptible and passible body, is without doubt necessary; but when it has been broken and dissolved and, at the time of the resurrection, the incorruptible has been rendered out of the corruptible and the spiritual out of the animal, no longer by the labor of affliction nor by the chastisement of abstinence, but by its own quality, no corruption will any longer have dominion over the body. So, therefore, even now the principle of abstinence seems necessary, and afterwards not to be sought. And in the third place you will find hidden in these things the secret sense of the mysteries of the wisdom and knowledge of God, by which the souls of the saints are nourished and fed not only in the present life, but also in that to come. For this is the priestly fruit, which is promised to those who hunger and thirst after righteousness, because they shall be filled. In this manner, therefore, in all the Scriptures the principle of this threefold sacrament runs its course. So also Wisdom admonishes that we should describe them for ourselves in our heart in a threefold way, "to answer," it says, "the word of truth to those who propose it to us." So Isaac the patriarch dug three wells, of which that third one alone is named by him "breadth" or "amplitude." But because the priestly sacrament is a rod of the nut, therefore I think that Jeremiah also, who was one of the priests from Anathoth, saw a nut rod and prophesied concerning it those things which are written either concerning the nut rod or concerning the caldron or pot set on fire, as if he showed by these that in the nut rod there is life and in the caldron set on fire there is death; for life and death are set before our face, and life indeed is Christ in the sacrament of the nut, but death is the devil in the figure of the caldron set on fire. If, therefore, you have sinned, you will place your portion with the caldron set on fire; but if you have acted justly, your portion will be made in the nut rod with the great high priest. But also in the Song of Songs the bride is said to go down into the garden of the nut, where too she is described as having found, together with the nuts, an abundance of priestly fruits, as it were. But nevertheless concerning the rods, as we had begun to say, God promised that one would sprout among the rods, and he gave more. But attend more carefully, in case perhaps we can teach that the liberality of God is more generous even than his own promises; in case perhaps from these things too we may be able to search out and investigate that ineffable goodness of God, which is always veiled in the letter of the Scripture, since we see him more generous in bestowing than in promising.
Source: HOMILIES ON NUMBERS 9.7