The interpretation timeline
Revelation 5:9 Douay-Rheims

And they sung a new canticle, saying: Thou art worthy, O Lord, to take the book, and to open the seals thereof; because thou wast slain, and hast redeemed us to God, in thy blood, out of every tribe, and tongue, and people, and nation.

A.D. 220 – 1871 7 witnesses

Patristic

before A.D. 750
220
A.D.
Tertullian Patristic
c. A.D. 150–220
“If I remember not that it is I who have served Him, how shall I ascribe glory to God? How sing to Him "the new song," if I am ignorant that it is I who owe Him thanks? But why is exception taken only against the change of the flesh, and not of the soul also, which in all things is superior to the flesh? How happens it, that the self-same soul which in our present flesh has gone through all life's course, which has learnt the knowledge of God, and put on Christ, and sown the hope of salvation in this flesh, must reap its harvest in another flesh of which we know nothing? Verily that must be a most highly favoured flesh, which shall have the enjoyment of life at so gratuitous a rate! But if the soul is not to be changed also, then there is no resurrection of the soul; nor will it be believed to have itself risen, unless it has risen some different thing.”
Source
303
A.D.
c. A.D. 250–303
“"Twenty-four elders and four living creatures, having harps and phials, and singing a new song." The proclamation of the Old Testament associated with the New, points out the Christian people singing a new song, that is, bearing their confession publicly. It is a new thing that the Son of God should become man. It is a new thing to ascend into the heavens with a body. It is a new thing to give remission of sins to men. It is a new thing for men to be sealed with the Holy Spirit. It is a new thing to receive the priesthood of sacred observance, and to look for a kingdom of unbounded promise. The harp, and the chord stretched on its wooden frame, signifies the flesh of Christ linked with the wood of the passion. The phial signifies the Confession, and the race of the new Priesthood. But it is the praise of many angels, yea, of all, the salvation of all, and the testimony of the universal creation, bringing to our Lord thanksgiving for the deliverance of men from the destruction of death. The unsealing of the seals, as we have said, is the opening of the Old Testament, and the foretelling of the preachers of things to come in the last times, which, although the prophetic Scripture speaks by single seals, yet by all the seals opened at once, prophecy takes its rank.”
Source

Post-Reformation

c. 1650 – 1900
1771
A.D.
John Gill Reformed
1697–1771
“And they sung a new song,.... Upon a new occasion and subject, redemption by the blood of the Lamb, and his worthiness to open the sealed book; and in distinction from the old song of Moses and the children of Israel at the Red sea; and this was a most famous and excellent song, an unheard of one, and which none could learn, or sing, but the redeemed of the Lamb: saying, thou art worthy to take the book, and open the seals thereof. The Arabic version reads, "thou, O Lamb"; the reasons why they ascribe such fitness, ability, and dignity to him, are as follow: for thou wast slain: by men, and for the sins of men; whereby, as he became worthy in his priestly office to take away the sins of his people, and to have all the glory of their salvation, and, in his kingly office, to have all power and authority, and to be exalted above every name, so, in his prophetic office, to have perfect knowledge, as man and Mediator, of all the future events that were to befall his church and people, and to make them known, and fulfil them: and hast redeemed us to God by thy blood, out of every kindred, and tongue, and people, and nation; this shows, that as the four living creatures, and four and twenty elders, were not angels, so they were not representatives of the Jewish church; or the patriarchs and prophets of the Old Testament; not even the apostles of the New; for they were all Jews, and could not be said to be redeemed out of every tongue, nation, and people; and also that not the Jews only were redeemed by Christ, but the Gentiles also, and not all mankind, or every individual of human nature, but some out of all the nations of the earth; for God hath chosen some, both of Jews and Gentiles, and these Christ has redeemed and therefore the Gospel is sent unto all nations, that these among them may be called and saved. The redemption of them supposes them to have been in a state of slavery and bondage, as they are by nature, to sin, Satan, and the law; and signifies a deliverance from such a state, which Christ has obtained, not barely by power, but by price, as the word here used signifies, and may be rendered, "and hast bought us" and the price with which he has bought them in his own "blood", and which is of full and sufficient value, it being not only the blood of a man, of an innocent man, but of one that is God as well as man: and this price was paid "to God", and to his justice, against whom men have sinned, whose law they have broken, and whose justice they have injured and affronted, that he might reconcile them to God, bring them near to him, and that they might serve him in righteousness and true holiness.”
Source
1832
A.D.
Adam Clarke Methodist
1762–1832
“A new song - Composed on the matters and blessings of the Gospel, which was just now opened on earth. But new song may signify a most excellent song; and by this the Gospel and its blessings are probably signified. The Gospel is called a new song, Psa 96:1. And perhaps there is an allusion in the harps here to Psa 144:9 : I will sing a New Song unto thee, O God: upon a Psaltery, and an Instrument of Ten Strings, etc. The same form of speech is found, Isa 42:10 : Sing unto the Lord a New Song, etc.; and there the prophet seems to have the Gospel dispensation particularly in view. Thou - hast redeemed us to God - out of every - nation - It appears, therefore, that the living creatures and the elders represent the aggregate of the followers of God; or the Christian Church in all nations, and among all kinds of people, and perhaps through the whole compass of time: and all these are said to be redeemed by Christ's blood, plainly showing that his life was a sacrificial offering for the sins of mankind.”
Source
1849
A.D.
1774–1849
“. They sung a new canticle, &c. called new, as belonging to the New Testament, or alliance of the new law of Christ. (Witham) — Canticle ; that is, excellent. The Scripture generally attaches the epithet new to canticles. New canticles are always more agreeable, says Pindar. (Grotius) — And hast redeemed, &c. The twenty-four ancients here may well represent all, who are in possession of beatitude. They all acknowledge it is to Jesus Christ they are indebted for the felicity they enjoy; it is he that has assembled at the foot of God’s throne all the nations of the world, faithful souls from every tribe and tongue, and people and nation, by his blood. (Calmet)”
Source
1871
A.D.
1871
“sung--Greek, "sing": it is their blessed occupation continually. The theme of redemption is ever new, ever suggesting fresh thoughts of praise, embodied in the "new song." us to God--So manuscript B, Coptic, Vulgate, and CYPRIAN. But A omits "us": and Aleph reads instead, "to our God." out of--the present election-church gathered out of the world, as distinguished from the peoples gathered to Christ as the subjects, not of an election, but of a general and world-wide conversion of all nations. kindred . . . tongue . . . people . . . nation--The number four marks world-wide extension: the four quarters of the world. For "kindred," translate as Greek, "tribe." This term and "people" are usually restricted to Israel: "tongue and nation" to the Gentiles (Rev 7:9; Rev 11:9; Rev 13:7, the oldest reading; Rev 14:6). Thus there is here marked the election-Church gathered from Jews and Gentiles. In Rev 10:11, for "tribes," we find among the four terms "kings"; in Rev 17:15, "multitudes."”
Source

Undated

date unknown
date
unknown
Glossa Ordinaria Medieval
“They sung a canticle. With exultation the Church professes the New Testament by work, while she baptizes into his death. Tribe. It is so called from three orders, in which there are seventy-two tongues, in each one of them; of which there are many peoples, and in a people, nations. Three orders of those to be saved: Noe, Daniel, Job. Or three orders of the nations: Greeks, Hebrews, Christians.”
Source
Modern · 1953 →

The in-app commentary runs from the Fathers to the early-modern record, then stops — that's where the public-domain sources end, not where the reading does. For the modern reading, follow the sources directly.