SQPN says that the Roman Catholic feast of Joel is July 13, but the Greek Orthodox celebrate him today. It's nice to have choices; today, we're going eastern.
Most sources claim not to know anything about Joel except that his father's name was Pethuel and he wrote a brief book included in the Tanach (Old Testament). It is a mere 73 verses, which allowed me to read it just before I wrote this. Talk about some fear of God! Joel basically gives the people of Judah (Judea, later) a couple of choices. In the first, waves of insects will devour all plant life, then brooks will dry up and the livestock will suffer. Then the army of The Lord will march in ranks across the land, burning everything and killing everyone. This is what comes of failing to keep the Law.
Alternatively, the people will keep the Law, praise The Lord, and be faithful. The crops will flourish. Vats of wine and oil will be brimming and the threshing floors will be piled high with grain. Eventually The Lord will bring his Kingdom to earth, summoning all the nations to the Valley of Jehoshaphat for judgment, and he will punish them for the wicked things they have done. But for the faithful, the mountains will drop down sweet wine, the hills will flow with milk, and the brooks of Judah will flow with waters.
Joel doesn't address the bad things / good people problem. It is a weakness in his text. Faithful, devout people also have bad stuff happen. It could be argued that no one is faithful and good enough, but then, one wonders why The Lord would set the bar so unattainably high? One might argue that it is not individuals, but rather the nation that is judged by The Lord, but that too seems unjust to those who keep the Law but cannot inspire their neighbors. Reading Joel, I can understand the market for the message offered by Jesus, Paul and the early Christians. Living under Roman occupation (following Hellenistic occupation), they understood that those least faithful to The Lord would be most prosperous. Conversely, those most faithful were distrusted, scorned, and abused. Since God was not delivering the nation from its powerful neighbors, a new covenant of individual salvation would be necessary. Believe in God, suffer on earth, and there will be a place for you in the Kingdom of God (details about where and when are debatable).
I am not giving much credit to Joel, but most of his book leaves me flat. In an attempt to be balanced (if not fair), let me note two memorable phrases associated with him. First, he picks up on Isaiah's "swords into plowshares" phrase, but instead imagines that The Lord will come to lead his people in triumph, saying,
Beat your plowshares into swords,
and your pruning hooks into spears.
Let the weak say, ‘I am strong.’ (Chapter 3, Verse 10)
He also describes The Lord inspiring the people directly, every man and woman becoming his or her own prophet. Saint Peter picks up on this passage when explaining the Pentecost.
It will happen afterward, that I will pour out my Spirit on all flesh;and your sons and your daughters will prophesy.
Your old men will dream dreams.
Your young men will see visions.
And also on the servants and on the handmaids in those days,
I will pour out my Spirit. Chapter 2, (Verses 28-29)
The editors of the Tanach might have ditched Joel, especially after he inverted Isaiah's promise of a peacetime economy (spears into pruning hooks). They, however, held true to their job and didn't boot him out, which is much to their credit.