48 But as it is incumbent on us to discuss this matter of the beast more exactly, and in particular the question how the Holy Spirit has also mystically indicated his name by means of a number, we shall proceed to state more clearly what bears upon him. John then speaks thus: “And I beheld another beast coming up out of the earth; and he had two horns, like a lamb, and he spoke as a dragon. And he exercised all the power of the first beast before him; and he made the earth and them which dwell therein to worship the first beast, whose deadly wound was healed.
And he did great wonders, so that he makes fire come down from heaven on the earth in the sight of men, and deceives them that dwell on the earth by means of those miracles which he had power to do in the sight of the beast, saying to them that dwell on the earth, that they should make an image to the beast which had the wound by a sword and did live. And he had power to give life unto the image of the beast, that the image of the beast should both speak, and cause that as many as would not worship the image of the beast should be killed.
And he caused all, both small and great, rich and poor, free and bond, to receive a mark in their right hand or in their forehead; and that no man might buy or sell, save he that had the mark, the name of the beast, or the number of his name. Here is wisdom. Let him that has understanding count the number of the beast; for if is the number of a man, and his number is six hundred threescore and six.”
Source: The Antichrist (New Advent)