3 In proceeding to make mention of these things, I shall adopt, to commend my undertaking, the pattern of Luke the Evangelist, saying on my own account: 'Forasmuch as some have taken in hand,' to reduce into order for themselves the books termed apocryphal, and to mix them up with the divinely inspired Scripture, concerning which we have been fully persuaded, as they who from the beginning were eyewitnesses and ministers of the Word, delivered to the fathers; it seemed good to me also, having been urged thereto by true brethren, and having learned from the beginning, to set before you the books included in the Canon, and handed down, and accredited as Divine; to the end that any one who has fallen into error may condemn those who have led him astray; and that he who has continued steadfast in purity may again rejoice, having these things brought to his remembrance.
Source: Letters (New Advent)