16 Such is not the Holy Ghost; God forbid! For His doings tend the contrary way, towards what is good and salutary. First, His coming is gentle; the perception of Him is fragrant; His burden most light; beams of light and knowledge gleam forth before His coming. He comes with the bowels of a true guardian: for He comes to save, and to heal, to teach, to admonish, to strengthen, to exhort, to enlighten the mind, first of him who receives Him, and afterwards of others also, through him.
And as a man, who being previously in darkness then suddenly beholds the sun, is enlightened in his bodily sight, and sees plainly things which he saw not, so likewise he to whom the Holy Ghost is vouchsafed, is enlightened in his soul, and sees things beyond man's sight, which he knew not; his body is on earth, yet his soul mirrors forth the heavens. He sees, like Esaias, the Lord sitting upon a throne high and lifted up; he sees, like Ezekiel, Him who is above the Cherubim; he sees like Daniel, ten thousand times ten thousand, and thousands of thousands; and the man, who is so little, beholds the beginning of the world, and knows the end of the world, and the times intervening, and the successions of kings—things which he never learned: for the True Enlightener is present with him.
The man is within the walls of a house; yet the power of his knowledge reaches far and wide, and he sees even what other men are doing.
Source: Catechetical Lectures (New Advent)