Jamieson, Fausset and Brown on Revelation 1:3

3. he that readeth, and they that hear--namely, the public reader in Church assemblies, and his hearers. In the first instance, he by whom John sent the book from Patmos to the seven churches, read it publicly: a usage most scriptural and profitable. A special blessing attends him who reads or hears the apocalyptic "prophecy" with a view to keeping the things therein (as there is but one article to "they that hear and keep those things," not two classes, but only one is meant: "they who not only hear, but also keep those things," Ro 2:13); even though he find not the key to its interpretation, he finds a stimulus to faith, hope, and patient waiting for Christ. Note: the term "prophecy" has relation to the human medium or prophet inspired, here John: "Revelation" to the Divine Being who reveals His will, here Jesus Christ. God gave the revelation to Jesus: He by His angel revealed it to John, who was to make it known to the Church.