For to him knowledge (_gnosis_) is the principal thing. Consequently, therefore, he applies to the subjects that are a training for knowledge, taking from each branch of study its contribution to the truth. Prosecuting, then, the proportion of harmonies in music; and in arithmetic noting the increasing and decreasing of numbers, and their relations to one another, and how the most of things fall under some proportion of numbers; studying geometry, which is abstract essence, he perceives a continuous distance, and an immutable essence which is different from these bodies. And by astronomy, again, raised from the earth in his mind, he is elevated along with heaven, and will revolve with its revolution; studying ever divine things, and their harmony with each other; from which Abraham starting, ascended to the knowledge of Him who created them. Further, the Gnostic will avail himself of dialectics, fixing on the distinction of genera into species, and will master[1027] the distinction of existences, till he come to what are primary and simple. But the multitude are frightened at the Hellenic philosophy, as children are at masks, being afraid lest it lead them astray. But if the faith (for I cannot call it knowledge) which they possess be such as to be dissolved by plausible speech, let it be by all means dissolved,[1028] and let them confess that they will not retain the truth. For truth is immoveable; but false opinion dissolves. We choose, for instance, one purple by comparison with another purple. So that, if one confesses that he has not a heart that has been made right, he has not the table of the money-changers or the test of words.[1029] And how can he be any longer a money-changer, who is not able to test and distinguish spurious coin, even offhand? Now David cried, “The righteous shall not be shaken for ever;”[1030] neither, consequently, by deceptive speech nor by erring pleasure. Whence he shall never be shaken from his own heritage. “He shall not be afraid of evil tidings;”[1031] consequently neither of unfounded calumny, nor of the false opinion around him. No more will he dread cunning words, who is capable of distinguishing them, or of answering rightly to questions asked. Such a bulwark are dialectics, that truth cannot be trampled under foot by the Sophists. “For it behoves those who praise in the holy name of the Lord,” according to the prophet, “to rejoice in heart, seeking the Lord. Seek then Him, and be strong. Seek His face continually in every way.”[1032] “For, having spoken at sundry times and in divers manners,”[1033] it is not in one way only that He is known.