Joel means Yahweh (Ya) is god (el) in Hebrew, which is a reverse of the order of the prophet Elijah's name - God (el) is Yahweh (Ya). Both make the case that there is but one God, and He is Israel's God, Yahweh. Both names, I think, are designed to call to mind the passage from Deuteronomy enshrined in Judaism's famous Shema prayer:

Deuteronomy 6:4–5

“Hear (Heb. Shema), O Israel: The LORD (Yahweh) our God, the LORD is one. You shall love the LORD your God with all your heart and with all your soul and with all your might." (ESV)

Jesus quotes this passage in all three synoptic gospels, so that its truth is fully established (Matthew 18:16).

We might say that the theme of Joel is The Day of the LORD - past, present, and future, and how we are to respond to it, even in the midst of the judgment:

Joel 2:12–14 “Yet even now,” declares the LORD, “return to me with all your heart, with fasting, with weeping, and with mourning; and rend your hearts and not your garments.” Return to the LORD your God, for he is gracious and merciful, slow to anger, and abounding in steadfast love; and he relents over disaster. Who knows whether he will not turn and relent, and leave a blessing behind him, a grain offering and a drink offering for the LORD your God? (ESV)

There is a great deal to think about in this book - a mix of past, present and future days of the LORD.

As usual, this summary of Joel may be useful as you read/listen to this book of God's word.

https://youtu.be/zQLazbgz90c?si=-Fho0nlpDqiqZxOH