I am he that liveth. This should be joined with what precedes. "I am the First and the Last, and the Living One; and I became dead, and behold I am alive forevermore, and I have the keys of death and of Hades."
"Became" or "came to be" ( ἐγενόμην), as in Revelation 1:9 and Revelation 1:10, indicates an exceptional condition. The "Amen" has been improperly inserted after "forevermore" (see on "forever and ever," in Revelation 1:6) from liturgical usage.
Most English versions omit it. The keys, as so often, are the sign of authority (Revelation 3:7; Revelation 9:1; Revelation 20:1; Matthew 16:19). Christ, as the absolutely Living One, who "has life in himself" and is the Source of life in others, has control, not merely over the passage from this world to the other, but over the other world itself.
He can recall departed souls from their resting place. The error of rendering αιδης "hell" has often been pointed out; it is not a place of punishment, but the temporary home of the departed, who are awaiting the day of judgment.
"Death," in all the best manuscripts and versions precedes "Hades;" and this is the logical order.