A.T. Robertson Commentary Revelation 1:18

"and the Living one; and I was dead, and behold, I am alive for evermore, and I have the keys of death and of Hades." — Revelation 1:18 (ASV)

And I was dead (κα εγενομην νεκρος). "And I be came dead" (aorist middle participle of γινομα as in 1:9,10, definite reference to the Cross).

I am alive (ζων ειμ). Periphrastic present active indicative, "I am living," as the words ο ζων just used mean.

Forevermore (εις τους αιωνας των αιωνων). "Unto the ages of the ages," a stronger expression of eternity even than in 1:6.

The keys (τας κλεις). One of the forms for the accusative plural along with κλειδας, the usual one (Matthew 16:19).

Of death and of Hades (του θανατου κα του αιδου). Conceived as in Mt 16:18 as a prison house or walled city. The keys are the symbol of authority, as we speak of honouring one by giving him the keys of the city. Hades here means the unseen world to which death is the portal. Jesus has the keys because of his victory over death. See this same graphic picture in 6:8; 20:13f. For the key of David see 3:7, for the key of the abyss see 9:1; 20:1.