8 And it came to pass, that on the morrow Moses went into the tabernacle of witness; and, behold, the rod of Aaron for the house of Levi was budded, and brought forth buds, and bloomed blossoms, and yielded almonds.
In the book of the prophet it is written: "Take to thyself the rod of an almond tree." We ought to consider why the Lord said this to the prophet, for it was not written without a purpose, since in the Pentateuch too we read that the almond rod of Aaron the priest, after being long laid up, blossomed. For the Lord seems to signify by the rod that the prophetic or priestly authority ought to be straightforward, and to advise not so much what is pleasant as what is expedient.
And so He Himself also chose Aaron as priest, that not the will of man but the grace of God should have the chief part in the election of the priest; not the voluntary offering of himself, nor the taking it upon himself, but the vocation from heaven, that he should offer gifts for sins who could be touched for those who sinned, for He Himself, it is said, bears our weakness. No one ought to take this honour upon himself but they are called of God, as was Aaron, and so Christ did not demand but received the priesthood.
For Paul came to preach the cross of the Lord, always green like the holly oak, and the nuts, which have a harder shell and a tender fruit, and rightly so, for the priestly rod of Aaron was a nut tree, and the staff of Jeremiah was of the same kind. Who would doubt that silver is also a dual-purpose, not idle gift; when both the life of the Patriarchs and the discourse of the Apostles always flourish in the hearts of individuals; and the speech of the saints, like silver tested by fire, shines with the bright light of salutary instruction? And not without reason do they refer to dual-purpose silver in which the coming of Paul was prefigured, who bestowed double honor on the laboring elders in word and doctrine.
There is only one true high priest, as Scripture says, of whom the high priest Aaron presented a figure. For this reason his rod blossomed. Just as Aaron’s rod sprouted among the Jewish people, so the cross of Christ flowered among the Gentiles. However, since Christ is the true high priest, as we have often said, he is the only one whose rod of the cross not only sprouted but also blossomed and produced the fruit of all believers.What is the fruit which it bore? “Ripe almonds.” Almonds are nuts, brethren. This fruit is bitter indeed in its first covering, is protected and defended by the second, but in the third part [it] feeds and nourishes whoever eats it. Such then is knowledge of the law and the prophets in Christ’s church. The first appearance of the letter is quite bitter, because it commands circumcision of the flesh, enjoins sacrifices and ordains other things which are designated as the killing letter. Throw away all these things as the bitter shell of the nut. In the second place, you will come to the protective covering, in which is indicated moral doctrine or the idea of self-restraint. This is necessary for the protection of what is kept inside but doubtless must sometimes be broken and destroyed. For example, fasting and chastisement of the body are no doubt necessary as long as we are in this corruptible body which is subject to suffering. However, when it has been destroyed and dissolved at the approach of death, it will become incorruptible at the time of the resurrection when it has been restored from corruption, spiritual after being natural, and without any flattery to the body will dominate, with no difficult suffering or propitiatory fasting but by its own nature. Thus then that rather hard covering of the nut seems to be a means of self-control at present that will not be sought later. Third, you will find hidden as in the nut the secret meaning of the mysteries of God’s wisdom and knowledge. With these, holy souls are nourished and fed not only in the present life but also in the future one. This is that priestly fruit concerning which it is promised to those “who hunger and thirst for justice, for they shall be satisfied.”
The rod of Aaron for the house of Levi, was budded: This rod of Aaron which thus miraculously brought forth fruit, was a figure of the blessed Virgin conceiving and bringing forth her Son without any prejudice to her virginity.
[AD 397] Ambrose of Milan on Numbers 17:8