13. a voice--literally, "one voice."
      from--Greek, "out of."
      the four horns--A, Vulgate (Amiatinus manuscript), Coptic, and Syriac omit "four." B and CYPRIAN support it. The four horns together gave forth their voice, not diverse, but one. God's revelation (for example, the Gospel), though in its aspects fourfold (four expressing world-wide extension: whence four is the number of the Evangelists), still has but one and the same voice. However, from the parallelism of this sixth trumpet to the fifth seal (Re 6:9, 10), the martyrs' cry for the avenging of their blood from the altar reaching its consummation under the sixth seal and sixth trumpet, I prefer understanding this cry from the four corners of the altar to refer to the saints' prayerful cry from the four quarters of the world, incensed by the angel, and ascending to God from the golden altar of incense, and bringing down in consequence fiery judgments. Aleph omits the whole clause, "one from the four horns."

JFB.