Revelation 11:1

And then she again took hold of me by the hand, and raised me, and made me sit on the seat to the left; and lifting up a splendid rod, she said to me, "Do you see something great?" And I said, "Lady, I see nothing."

"And there was shown unto me a reed like unto a rod: and the angel stood, saying, Rise, and measure the temple of God, and the altar, and them that worship therein." A reed was shown like to a rod. This itself is the Apocalypse which he subsequently exhibited to the churches; for the Gospel of the complete faith he subsequently wrote for the sake of our salvation. For when Valentinus, and Cerinthus, and Ebion, and others of the school of Satan, were scattered abroad throughout the world, there assembled together to him from the neighbouring provinces all the bishops, and compelled him himself also to draw up his testimony. Moreover, we say that the measure of God's temple is the command of God to confess the Father Almighty, and that His Son Christ was begotten by the Father before the beginning of the world, and was made man in very soul and flesh, both of them having overcome misery and death; and that, when received with His body into heaven by the Father, He shed forth the Holy Spirit, the gift and pledge of immortality, that He was announced by the prophets, He was described by the law, He was God's hand, and the Word of the Father from God, Lord over all, and founder of the world: this is the reed and the measure of faith; and no one worships the holy altar save he who confesses this faith.

When he says “Rise,” he arouses the church, for John, who is an image of the church, did not hear these things sitting down but standing up. “Measure,” it says, “the temple and the altar and those who worship there.” He did not command that everyone be measured; rather, he commanded that a portion be prepared unto the end [time], so that what is said in the Gospel might be fulfilled, “Many are called, but few are chosen.” “But do not measure the court outside the temple, leave that out.” The court, which is outside the temple, although it seems to belong to the temple, in fact is not the temple, for it has no relation to the holy of holies. These are those persons who appear to be in the church but are outside of it.… Those persons who are outside the temple are also the nations who have never believed the gospel of the Lord. Both groups will trample his church.

In the visions that had come before, the apparition revealed to the divine John the multitude of saints accompanying Christ and the divine throne they beheld, among whom those from the nations far outnumbered those from Israel. But now, another vision shows him how many, or rather how few, were esteemed in the time of the Old Covenant, and how many in the era of the New.

And see how cleverly this is depicted to him. He is given a measuring rod to measure the temple of God and the altar within the temple, clearly referring to the one in Jerusalem, and those who worship there. And he measured; for those who were counted were few, as in the times of old, who had found favor with God.

He commands that the teaching of a false faith and the contagion of a sinful way of life among the heretics, Jews and Gentiles be expelled, for it is not right that such persons approach the holy of holies. For the apostle says, “What have I to do with judging outsiders? Is it not those inside whom you are to judge?” When all the Jews, heretics, and Gentiles incessantly attack the church by all means available, it is as though they are trampling upon the church. The number of the months signifies not only the time of the last persecution but also the entire time of Christianity. For there are six ages of the world and seven days by which all time moves by passing away and returning. Six times seven makes forty-two, and I believe that the passage refers to both of these [numbers].

We think that the church is called the “temple of the living God,” for in it we offer spiritual sacrifices to God. And I think that the “court outside” is the assembly of the unbelieving Gentiles and Jews, and so by virtue of their impiety they are unworthy to be measured by the angel. “For the Lord knows those who are his,” as it says, but he who knows all things is said not to know the transgressors. That the holy city, whether that be the new Jerusalem or the catholic church, will be trampled by the nations for forty-two months signifies, I believe, that at the appearance of the antichrist those who are faithful and trustworthy will be trampled and persecuted for three and a half years.

And a reed like a rod was given to me. In the reed, he received the ministry of writing the Gospel, which is not superfluous in vain elegance, but like a rod of righteousness, the rod of the kingdom of God (Hebrews I). For he describes the eternal kingdom of Christ.

And those who worship in it. Because not all who seem to worship in it do so, just as he who confesses me. Finally, he commands that a part not be counted, saying:

Rise and measure the temple of God and the altar. He said rise, not because John was hearing these things while sitting, but because with this word he rouses the hearts of each one to measure the evangelical Scripture and deeds. For there they find how much each one advances and how much they conform to the divine rule.

And there was given me a reed like unto a rod, saying: Arise, and measure the temple of God, and the altar and them that adore therein. He says this in the person of preachers in general. The reed represents metaphorically the divine preaching written by it, and it is called like unto a rod because holy preaching is not pliant but straight. The temple of God is the faithful, to whom it is said, You are the temple of the living God. [2 Cor. 6:16] The altar in the temple is the life of the religious among the people of the faithful, in whom the fire of holy devotion principally and continuously remains without declining. By them that adore therein he means in the temple and the altar, words by which they that adore therein are themselves represented. So, what does it mean to measure the temple and the altar with a reed, if not to bestow the grace of gifts through holy preaching? Which the Church certainly does in Christ, that is in its Head. Note also that he who must measure the temple of God, is told to arise, that is, to rise to high summits of virtues through the practice of work, so as to become higher than the building he is measuring.