1 And the LORD spake unto Moses, saying, 2 Speak unto the children of Israel, and take of every one of them a rod according to the house of their fathers, of all their princes according to the house of their fathers twelve rods: write thou every man's name upon his rod. 3 And thou shalt write Aaron's name upon the rod of Levi: for one rod shall be for the head of the house of their fathers. 4 And thou shalt lay them up in the tabernacle of the congregation before the testimony, where I will meet with you. 5 And it shall come to pass, that the man's rod, whom I shall choose, shall blossom: and I will make to cease from me the murmurings of the children of Israel, whereby they murmur against you. 6 And Moses spake unto the children of Israel, and every one of their princes gave him a rod apiece, for each prince one, according to their fathers' houses, even twelve rods: and the rod of Aaron was among their rods. 7 And Moses laid up the rods before the LORD in the tabernacle of witness. 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. 9 And Moses brought out all the rods from before the LORD unto all the children of Israel: and they looked, and took every man his rod. 10 And the LORD said unto Moses, Bring Aaron's rod again before the testimony, to be kept for a token against the rebels; and thou shalt quite take away their murmurings from me, that they die not. 11 And Moses did so: as the LORD commanded him, so did he. 12 And the children of Israel spake unto Moses, saying, Behold, we die, we perish, we all perish. 13 Whosoever cometh any thing near unto the tabernacle of the LORD shall die: shall we be consumed with dying?
[AD 397] Ambrose of Milan on Numbers 17:8
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.

[AD 397] Ambrose of Milan on Numbers 17:8
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.

[AD 397] Ambrose of Milan on Numbers 17:8
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.

[AD 407] John Chrysostom on Numbers 17:2
We can also learn from other sources how awesome was the dignity of the priesthood. Indeed, there was a day when some wicked and evil men revolted against Aaron, quarreled with him over his position in the community and tried to drive him from his leadership. Moses, the mildest of men, wanted to persuade them by the facts themselves that he had not brought Aaron to the leadership because he was a brother, relative or member of his family but that it was in obedience to God’s decree that he had entrusted the priesthood to him. So he ordered each tribe to bring a staff, and Aaron was instructed to do the same.When each tribe had brought a staff, Moses took all of them and put them inside the meeting tent. Once he had put them there, he gave orders that they await the decision of God which would come to them through those staves. Then all the other staves kept their same appearance, but a single one—Aaron’s—blossomed and put forth leaves and fruit. So the Lord of nature used leaves instead of letters to teach them that he had again elected Aaron.

[AD 542] Caesarius of Arles on Numbers 17:8
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.”

[AD 1781] Richard Challoner on Numbers 17:8
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.