From First and Second Timothy, Titus by George T. Montague, commenting on 1 Timothy 6:11-16
In affirming that God alone has immortality Paul is not thinking of the angels here or the glorified body of Christians (1 Cor 15:53–54) but of the pretenses of emperors to what God alone possesses.
Despite their humanness, emperors like Tiberius and Caligula were held to be immortal. Already in the Old Testament, light is one of the things most associated with divinity. God creates light and in that light creates everything else (Gen 1:3). Light dwells with him (Dan 2:22). He robes himself with light (Ps 104:2). He is light (1 John 1:5) and the Father of lights (James 1:17). This light makes him unapproachable to the human eye, like a mountain that cannot be scaled: “no man sees me and still lives” (Exod 33:20); “none can see him, however wise their hearts” (Job 37:24); “no one has ever seen God” (John 1:18).
The New Testament holds out the assurance that the faithful in the future life will enjoy the light of God (Rev 22:5) because they will see him face to face; but in this life even they see darkly and imperfectly (1 Cor 13:12). This is quite a contrast to the mortal emperors frequently shown with rays of light shining from their heads. The finale acclaims the one to whom all honor and eternal power belong.