From about the reign of Uzziah and onward, as already remarked (ch. 15. 12), the prophets began, under the guidance of the Holy Spirit, to reduce their prophecies to writing, and thus arose the series of _prophetical books_ that form a prominent part of the Old Testament canon. Their office is at once recognized by every reader as distinct from that of either the Pentateuch or the historical books; although these latter were, as a general rule, written by prophets also. (4.) There is a class, more miscellaneous in character, that may be described in general terms as the _poetical books_, in which the elements of meditation and reflection predominate. It includes the book of Job, which has for its theme divine providence, as viewed from the position of the Old Testament; the book of Psalms, that wonderful treasury of holy thought and feeling embodied in sacred song for the use of God's people in all ages; the book of Proverbs, with its inexhaustible treasures of practical wisdom; the book of Ecclesiastes, having for its theme the vanity of this world when sought as a satisfying good; and the book of Canticles, which the church has always regarded as a mystical song having for its ground-idea, under the Old Testament, that God is the husband of Zion, and under the New, that the church is the bride of Christ. How high a place this division of the canon holds in the system of divine revelation every pious heart feels instinctively. Without it, the revelation of the Old Testament could not have been complete for the work assigned to it. 5. We have seen the relation of the Old Testament as a whole to the entire system of revelation, and also the place occupied by its several divisions. It will further appear, as we proceed, that each particular book in these divisions contributes its share to the perfection of the whole.