“Return to Yahweh your God, for he is gracious and compassionate, slow to anger and abounding in love.” (Joel 2: 13)
"Many of the specific descriptions of judgment that the prophets proclaim on Israel and Judah come directly from Deuteronomy 28. Much of Joel’s message is closely connected to his extensive description of a locust plague. Thus Joel appears to draw directly from the warning judgment of Deuteronomy 28: 38, 42, 'You will sow much seed in the field but you will harvest little, because locusts will devour it… Swarms of locusts will take over all your trees and the crops of your land.' Unlike most of the other prophets, Joel skips the first point of the standard prophetic message ('You have broken the covenant'— idolatry, social injustice, religious formalism), apparently assuming the broken covenant. He does frequently call for repentance as he focuses on point two, 'Judgment,' and then moves to point three, 'Future hope and restoration.' That is, Joel skips over listing the many covenant violations and simply focuses on the resultant curse from Deuteronomy, apparently assuming that his audience is well aware of their guilt. He does, however, include a call to repent as well as a picture of future restoration and a section of judgment on the nations.
Structurally, the book of Joel breaks down into two halves, with 2: 18 functioning as the hinge. Each of the two halves also contains two units. Thus the structure is as follows:
I. The Judgment.
a. 1: 2 – 20 The coming locust invasion (perhaps a near view),
and a call to repentance.
b. 2: 1 – 17 The coming locust invasion (perhaps a far view), and
a call to repentance.
II. Yahweh’s response
a. 2: 18 – 32 Future restoration (the giving of Yahweh’s Spirit).
b. 3: 1 – 21 Judgment on the nations.
House suggests that Joel continues the central focus on 'warning' that unites the first six books (Hosea to Micah) within the Book of the Twelve. Yet Joel also reminds the readers that Yahweh is slow to anger and that he will always relent if his people will only repent. In this sense Joel reflects the theology of Hosea 1 – 2 and tempers the focus on judgment coming in Amos."
 Paul House, “The Character of God in the Book of the Twelve,” in James D. Nogalski and Marvin A. Sweeney, Reading and Hearing the Book of the Twelve, SBL Symposium Series 15 (Atlanta: Society of Biblical Literature, 2000), 131 – 32.
 Longman III, Tremper; Hays, J. Daniel (2010-09-21). The Message of the Prophets: A Survey of the Prophetic and Apocalyptic Books of the Old Testament (Kindle Locations 3907-3926). Zondervan. Kindle Edition.