"It is he alone who has immortality and dwells in unapproachable light, whom no one has ever seen or can see; to him be honor and eternal dominion. Amen."
The reference is to God as the Christ, the indwelling divinity that is the true identity of each of us. The light in which the Christ dwells cannot be seen by mortal eyes. It is the spiritual Truth that forms the basis of Jesus' teachings.