Adam Clarke on Revelation 6:8

A pale horse - The symbol of death. Pallida mors, pale death, was a very usual poetic epithet; of this symbol there can be no doubt, because it is immediately said, His name that sat on him was Death.

And hell followed with him - The grave, or state of the dead, received the slain. This is a very elegant prosopopaeia, or personification.

Over the fourth part of the earth - One fourth of mankind was to feel the desolating effects of this seal.

To kill with sword - War; with hunger - Famine; with death - Pestilence; and with the beasts of the earth - lions, tigers, hyenas, etc., which would multiply in consequence of the devastations occasioned by war, famine, and pestilence.