Jamieson, Fausset and Brown on Revelation 5:4

4. and to read--inserted in English Version Greek text without good authority. One oldest manuscript, Origen, Cyprian, and Hilary omit the clause. "To read" would be awkward standing between "to open the book" and "to look thereon." John having been promised a revelation of "things which must be hereafter," weeps now at his earnest desire being apparently frustrated. He is a pattern to us to imitate, as an eager and teachable learner of the Apocalypse.