The little book of Joel, so seldom read, contains some very interesting insights and some fine racy writing. The assertion that God uses Israel's foes to execute judgement upon His erring, faithless people runs through this, as well as the other, prophetic books.
What is probably the unique message of this book is first the
idea of the wholesale destruction and disaster that overwhelms
not only the people, but also the natural environment; secondly
the theme of judgement the "Day of the Lord" so vividly
foretold; thirdly the pouring out of God's Spirit upon those who
repent and are redeemed - a theme taken up in the New Testament
Joel 1.v.1 to 2.v.29