11 And I beheld, and I heard the voice of many angels round about the throne and the beasts and the elders: and the number of them was ten thousand times ten thousand, and thousands of thousands;
[AD 990] Oecumenius on Revelation 5:8-12
All worshiped the Lord after he had taken the scroll, since they already knew the salvation which he was going to effect for human beings and the punishment he was going to bring on the polluted demons.

The elders’ holding harps indicates the harmony and concord of their confession of God, according to Scripture, “Sing praises to our God, sing praises.”

The incense symbolizes the offering of all the nations, for Malachi, speaking in the person of God, says to disobedient Israel, “I will not accept an offering from your hand, for from the rising of the sun to its setting my name has been glorified among the nations, and in every place incense is offered in my name, and a pure sacrifice,” predicting by these [words] the faith of the nations and their bringing of gifts.

And they sing a new song: for the song sung to God incarnate is new, since it had never been invented before the incarnation.

What was the song? You are worthy, he says, to effect this salvation for human beings, you who were slain for us, and with your blood you took possession of many from among those under heaven.

Very correctly he said from every tribe and tongue and people and nation: for he did not acquire possession of everyone (for many died in unbelief), but only those who were worthy of salvation. The prophet also said something similar, “Arise, O God, judge the earth, because you” will place “your inheritance among all the nations,” where he does not simply say “all the nations.”

And he made them kings and priests to our God, and they shall reign on earth. You can indeed understand this literally, for the kings and presidents of the churches are [God’s] faithful people and servants of Christ. But you can also understand kings to be those who control their passions and are not controlled by them. And you can understand priests to be those who present their own persons “as a living sacrifice, holy and acceptable to God,” as Scripture says.

And he says not only the elders but also the incorporeal powers of the angels were singing a triumphant song to Christ. Daniel also predicted their number as now mentioned. The song of the angels attributes seven different honors to Christ, because by the number seven they indicate that it is fitting for Christ to be crowned with ten thousand praises.

[AD 542] Caesarius of Arles on Revelation 5:11-13
This is not said of his Godhead, in which are all the treasuries of wisdom, so that he should receive [wisdom]. Rather, this is said of his assumed manhood, that is, concerning his body, which is the church. Or, it might be said of his martyrs who were slain for his name. For the church receives all things in her Head, as the Scriptures say, “He has given us all things with him.” The Lamb himself receives, as he said in the Gospel, “All authority in heaven and on earth has been given to me.” However, he receives [this authority] according to his humanity, not according to his divinity.

[AD 614] Andreas of Caesarea on Revelation 5:11-13
From all beings, whether intelligent or sensible, whether living or simply existing in some way, God, as the Creator of all things, is glorified by words proper to their natures. Also praised is his only begotten and consubstantial Son who graciously renewed humankind and the creation that was made through him. And it is written that, as man, he received authority over all things in heaven and upon the earth.

[AD 735] Bede on Revelation 5:11
And their number was thousands upon thousands. Innumerable thousands of people flocking to the Church praise God.