Arthur E. Waite - The Pictorial Key to the Tarot :
The veil or mask of life is perpetuated in change, transformation and passage from lower to higher, and this is more fitly represented in the rectified Tarot by one of the apocalyptic visions than by the crude notion of the reaping skeleton. Behind it lies the whole world of ascent in the spirit.
The mysterious horseman moves slowly, bearing a black banner emblazoned with the Mystic Rose, which signifies life. Between two pillars on the verge of the horizon there shines the sun of immortality. The horseman carries no visible weapon, but king and child and maiden fall before him, while a prelate with clasped hands awaits his end.
There should be no need to point out that the suggestion of death which I have made in connection with the previous card is, of course, to be understood mystically, but this is not the case in the present instance.
The natural transit of man to the next stage of his being either is or may be one form of his progress, but the exotic and almost unknown entrance, while still in this life, into the state of mystical death is a change in the form of consciousness and the passage into a state to which ordinary death is neither the path nor gate.
The existing occult explanations of the 13th card are, on the whole, better than usual, rebirth, creation, destination, renewal, and the rest.
P. D. Ouspensky – The Symbolism Of The Таrot :
Fatigued by the flashing of the Wheel of Life, I sank to earth and shut my eyes. But it seemed to me that the Wheel kept turning before me and that the four creatures continued sitting in the clouds and reading their books.
Suddenly, on opening my eyes, I saw a gigantic rider on a white horse, dressed in black armour, with a black helmet and black plume. A skeleton's face looked out from under the helmet. One bony hand held a large, black, slowly-waving banner, and the other held a black bridle ornamented with skulls and bones.
And, wherever the white horse passed, night and death followed; flowers withered, leaves drooped, the earth covered itself with a white shroud; graveyards appeared; towers, castles and cities were destroyed.
Kings in the full splendour of their fame and their power; beautiful women loved and loving; high priests invested by power from God; innocent children--when they saw the white horse all fell on their knees before him, stretched out their hands in terror and despair, and fell down to rise no more.
Afar, behind two towers, the sun sank.
A deadly cold enveloped me. The heavy hoofs of the horse seemed to step on my breast, and I felt the world sink into an abyss.
But all at once something familiar, but faintly seen and heard, seemed to come from the measured step of the horse. A moment more and I heard in his steps the movement of the Wheel of Life!
An illumination entered me, and, looking at the receding rider and the descending sun, I understood that the Path of Life consists of the steps of the horse of Death.
The sun sinks at one point and rises at another. Each moment of its motion is a descent at one point and an ascent at another. I understood that it rises while sinking and sinks while rising, and that life, in coming to birth, dies, and in dying, comes to birth.
"Yes," said the voice. The sun does not think of its going down and coming up. What does it know of earth, of the going and coming observed by men? It goes its own way, over its own orbit, round an unknown Centre. Life, death, rising and falling--do you not know that all these things are thoughts and dreams and fears of the Fool"?