Book IV. ———————————— Argument—Passing to the second part of his work, that which treats of expression, the author premises that it is no part of his intention to write a treatise on the laws of rhetoric.  These can be learned elsewhere, and ought not to be neglected, being indeed specially necessary for the Christian teacher, whom it behoves to excel in eloquence and power of speech.  After detailing with much care and minuteness the various qualities of an orator, he recommends the authors of the Holy Scriptures as the best models of eloquence, far excelling all others in the combination of eloquence with wisdom.  He points out that perspicuity is the most essential quality of style, and ought to be cultivated with especial care by the teacher, as it is the main requisite for instruction, although other qualities are required for delighting and persuading the hearer.  All these gifts are to be sought in earnest prayer from God, though we are not to forget to be zealous and diligent in study.  He shows that there are three species of style, the subdued, the elegant, and the majestic; the first serving for instruction, the second for praise, and the third for exhortation:  and of each of these he gives examples, selected both from scripture and from early teachers of the church, Cyprian and Ambrose.  He shows that these various styles may be mingled, and when and for what purposes they are mingled; and that they all have the same end in view, to bring home the truth to the hearer, so that he may understand it, hear it with gladness, and practise it in his life.  Finally, he exhorts the Christian teacher himself, pointing out the dignity and responsibility of the office he holds to lead a life in harmony with his own teaching, and to show a good example to all.