Verse 2: And I saw a strong angel proclaiming with a loud voice, Who is worthy to open the book, and to loose the seals thereof?
[A strong Angel, ἰσχυρὸν] אֵל/el, a mighty one, which name is given to great Angels. See on Revelation 10:1; 18:21. These were great Angels: but certain things are reserved for Christ. In the Old Testament, God executed all things through Angels; in the New Testament, the chief things through Christ. Now, the greater the thing done, the greater the Angel ministering (Grotius). This was Gabriel (Lyra), or, one of the first rank (Tirinus, similarly Ribera). Angels, even the greatest, marvel at the economy of God in the Church, and earnestly desire to understand it, and to be serviceable to it (Durham).
[Proclaiming, etc.] As in Daniel 3:4 (Grotius). With the voice of a herald, etc. (Forbes).
A stong angel: There were no weak angels, but possibly this angel might, in appearance to John, look as if he were stronger than others; or rather, so judged from the great and loud voice he used.
[Who is worthy (that is, who is able [Menochius], who is furnished with Divine authority [Pareus]) to open, etc., ἀνοῖξαι—καὶ λῦσαι, etc.] That is, ἀνοῖξαι λυσάμενον, to open the book having been loosed: for the Book, or the parts of the Book, were not able to be opened, except with the Seal also broken. You have similar things in συνδέτοις/bands elsewhere, as in Colossians 2:19, with the passage in Acts 8:23 compared (Grotius). Who may open that book and loosen, etc.? (Beza, Piscator, etc.), that is, Who may open the Book by breaking its seals (Menochius). Now, this is proclaimed, not as if it was expected that this might be done be a creature (Durham); but partly so that the impotence and unworthiness of the creature might be exposed (Durham, similarly Forbes) to penetrate into the secrets of God, partly for the Mediator’s greater glory, etc. (Durham).
Who is worthy to open the book, and to loose the seals thereof? Not that he thought any was able, or worthy. We can only conclude from hence the impotency of men to search, and find out, and expound the deep things of God, and consequently the unlawfulness of too narrow a prying into his secret mysteries.
 Greek: καὶ εἶδον ἄγγελον ἰσχυρὸν κηρύσσοντα φωνῇ μεγάλῃ, Τίς ἐστιν ἄξιος ἀνοῖξαι τὸ βιβλίον, καὶ λῦσαι τὰς σφραγῖδας αὐτοῦ;  Revelation 10:1: “And I saw another mighty angel (ἄλλον ἄγγελον ἰσχυρὸν) come down from heaven, clothed with a cloud: and a rainbow was upon his head, and his face was as it were the sun, and his feet as pillars of fire…”  See 1 Peter 1:12.  See Psalm 91:11; Hebrews 1:14.  Colossians 2:19: “And not holding the Head, from which all the body by joints and bands (συνδέσμων) having nourishment ministered, and knit together, increaseth with the increase of God.”  Acts 8:23: “For I perceive that thou art in the gall of bitterness, and in the bond (σύνδεσμον) of iniquity.”