But what need is there to quote any more passages against Celsus, in order to prove that his words contain nothing which was not said long before among themselves, since that has been sufficiently established by what we have said? It seems that what follows has some reference to this: “If you think that a Divine Spirit has descended from God to announce divine things to men, it is doubtless this same Spirit that reveals these truths; and it was under the same influence that men of old made known many important truths.”
But he does not know how great is the difference between those things and the clear and certain teaching of those who say to us, “Your incorruptible spirit is in all things, wherefore God chastens them little by little that offend;” and of those who, among their other instructions, teach us that words, “Receive the Holy Ghost,” refer to a degree of spiritual influence higher than that in the passage, “You shall be baptized with the Holy Ghost not many days hence.” But it is a difficult matter, even after much careful consideration, to perceive the difference between those who have received a knowledge of the truth and a notion of God at different intervals and for short periods of time, and those who are more fully inspired by God, who have constant communion with Him, and are always led by His Spirit.
Had Celsus set himself to understand this, he would not have reproached as with ignorance, or forbidden us to characterize as “blind” those who believe that religion shows itself in such products of man's mechanical art as images. For every one who sees with the eyes of his soul serves the Divine Being in no other way than in that which leads him ever to have regard to the Creator of all, to address his prayers to Him alone, and to do all things as in the sight of God, who sees us altogether, even to our thoughts.
Our earnest desire then is both to see for ourselves, and to be leaders of the blind, to bring them to the Word of God, that He may take away from their minds the blindness of ignorance. And if our actions are worthy of Him who taught His disciples, “You are the light of the world,” and of the Word, who says, “The light shines in darkness,” then we shall be light to those who are in darkness; we shall give wisdom to those who are without it, and we shall instruct the ignorant.
Source: Against Celsus (New Advent)