The book of Isaiah marks the beginning of the so-called major prophets, a division that also takes in Jeremiah, Ezekiel, and Daniel.
The minor prophets (minor merely because they are shorter) follow, from Hosea to Malachi. With the failure of the priesthood (1 Sam. 1-4), the prophet, by God’s sovereign appointment, became the means whereby He could address Himself to the conscience of His people. The priest was the people’s representative before Jehovah; the prophet was Jehovah’s mouthpiece to the people.
Prophecy presents the mind of God, not just with respect to future events, but also as to present state. It is for this reason that the books of Joshua through Kings are to be found in the Hebrew Scriptures within the portion known as “The Prophets” (Luke 24:44).
Prophecy is two-sided. On the one hand, it reveals the sinful state of the people and God’s judgment—His strange work (Isa. 28:21). On the other hand, it reveals His heart in love, in particular the promise of the coming of the Messiah. One cannot be without the other.