The book of Joel is written like a poem. The prophet sat down to write it in a certain style. You do not just make up a poem. You need to mull it over, puzzle it out, and consider it carefully. It needs metre, assonances, poetic words, etc. Sometimes there are pieces in this book written in plain language: in prose. That is where Joel changes the normal style. Prose is found in Joel 2:12–14 (also Joel 2:18–20, Joel 2:25–27; Joel 3:1–8). The alternation in style is not without significance. The pieces of prose are bits that (broadly) describe God himself taking action. In all other places, Joel uses poetic language in his book. In this way he wants to convey his message and have it preserved for God’s people of all ages. It needs to be read as well as recited. That is what Joel had in mind with the forms he chose.
12 Maintenant encore, dit l'Eternel, Revenez à moi de tout votre cœur, Avec des jeûnes, avec des pleurs et des lamentations!