Joel describes the LORD as “gracious and merciful,” “slow to anger,” and “abounding in steadfast love.” He also says the LORD “relents over disaster.” See Joel 2:13.
In Joel 2:12–14, Yahweh calls the people to come back to him immediately and wholeheartedly. The return he wants is not mainly public display but inward honesty, shown through fasting, tears, and grief. The reason given is Yahweh’s own character: he is kind, compassionate, patient, and ready to hold back disaster. These verses sit after a terrifying description of an advancing disaster and the alarm of “the day of Yahweh” (2:1–11), where the community is confronted with urgency and vulnerability.
Joel 2:12–14 presents a direct divine appeal in a crisis setting: despite looming disaster, “yet even now” there is still time to return to turn to Yahweh. The return is described as total (“with all your heart”) and as inwardly real (“tear your heart, not your garments”).
A careful answer keeps the immediate passage, the book's argument, and the whole-Bible storyline together, so the question is answered in context instead of as a detached idea.
Start with Joel 2:13, then read the surrounding section so the answer stays connected to the passage's flow.
13Tear your heart, and not your garments, And turn to Yahweh, your God; For he is gracious and merciful, Slow to anger, and abundant in lovingkindness, And relents from sending calamity.