having six wings
The cherubim Ezekiel saw had four wings (Eze. Eze. 1:11-12) whereas these creatures have six wings like the seraphim which Isaiah saw attending the throne (Isa. Isa. 6:2, Isa. 6:6). In Isa. Isa. 6:2 we read, Each had six wings: with twain he covered his face (in reverence, as not presuming to lift up his face to God), with twain he covered his feet (in humility, as not worthy to stand in Gods holy presence), and with twain he did fly [in obedient readiness to do instantly Gods command]. 1
full of eyes
Eyes indicate great intelligence (Eze. Eze. 1:18; Eze. 10:12; Dan. Dan. 7:8, Dan. 7:20; Rev. Rev. 1:14+; Rev. 2:18+; Rev. 5:6+; Rev. 19:12+). These creatures are near the apex of Gods created order (Eze. Eze. 28:12-15).2
around and within
Johns object is to show that the six wings in each did not interfere with that which he had before declared, namely, that they were full of eyes before and behind. The eyes were round the outside of each wing, and up the inside of each when half expanded, and of the part of body in that inward recess.3 Being so full of eyes positioned in this manner, they are able to move their wings without ever disrupting their vision.4
Holy, holy, holy
Isaiahs seraphim made a similar pronouncement concerning Gods uniqueness (Isa. Isa. 6:3). Praises of Gods holiness are said to enthrone Him (Ps. Ps. 22:3). Who is like You, O LORD, among the gods? Who is like You, glorious in holiness, fearful in praises, doing wonders? (Ex. Ex. 15:11). Worship of God is a major theme of this book as He brings about the redemption of creation in the culmination of history. See Worship of God. Three denotes completeness or may reflect the Trinity. See Three: Life, Resurrection, Completeness, the Trinity.
Who was and is and is to come
ὁ ἦν καὶ ὁ ω῍ν καὶ ὁ ἐρχόμενος [ho ēn kai ho ōn kai ho erchomenos] , the same phrase as is found in Revelation Rev. 1:4+, Rev. 1:8+, but with the 1st and 2nd titles reversed. Comprised of a verb and two participles: The he was and the who is and the coming one. This unusual grammatical construction is discussed in the commentary on Revelation 1:4.
1 A. R. Fausset, The Revelation of St. John the Divine, in Robert Jamieson, A. R. Fausset, and David Brown, A Commentary, Critical and Explanatory, on the Old and New Testaments (Oak Harbor, WA: Logos Research Systems, Inc., 1997, 1877), Rev. 4:8.