The inquiry is prosecuted respecting knowledge, in which, as distinguished from wisdom, Augustin had begun in the former book to look for a kind of trinity. And occasion is taken of commending Christian faith, and of explaining how the faith of believers is one and common. Next, that all desire blessedness, yet that all have not the faith whereby we arrive at blessedness; and that this faith is defined in Christ, who in the flesh rose from the dead; and that no one is set free from the dominion of the devil through forgiveness of sins, save through Him. It is shown also at length that it was needful that the devil should be conquered by Christ, not by power, but by righteousness. Finally, that when the words of this faith are committed to memory, there is in the mind a kind of trinity, since there are, first, in the memory the sounds of the words, and this even when the man is not thinking of them; and next, the mind's eye of his recollection is formed thereupon when he thinks of them; and, lastly, the will, when he so thinks and remembers, combines both.