In the first vision of Jesus in Revelation he says, "I am the Alpha and the Omega, who is, and who was and who is to come." (1:8) Identifying himself as the first and last letters of the Greek alphabet expresses Christ's reign from the very beginning to the end of the world. "I AM" is the name God revealed to Moses in the Burning Bush. Here and elsewhere that name is developed into "who is and who was and who is to come."
It is a vision of a Christ who reigns from all eternity into all eternity.