Joel 2:12-13
Therefore also now, saith the LORD, turn ye even to me with all your heart, and with fasting, and with weeping, and with mourning: And rend your heart, and not your garments, and turn unto the LORD your God: for he is gracious and merciful, slow to anger, and of great kindness, and repenteth him of the evil.
Exodus 34:6
And the LORD passed by before him, and proclaimed, The LORD, The LORD God, merciful and gracious, longsuffering, and abundant in goodness and truth,
Joel 2:13's 'rend your heart, not your garments' pairs the Deuteronomy 30 return-with-whole-heart statute with the Exodus 34 divine character declaration as the ground for returning. The basis for returning — 'he is gracious and merciful, slow to anger, of great kindness' — quotes the Exodus 34 Sinai name-proclamation. Joel combines both Torah frameworks: the statute that commands return and the divine character that makes return possible.
Joel 2:15-16
Blow the trumpet in Zion, sanctify a fast, call a solemn assembly: Gather the people, sanctify the congregation, assemble the elders, gather the children, and those that suck the breasts:
Leviticus 23:27
Also on the tenth day of this seventh month there shall be a day of atonement: it shall be an holy convocation unto you; and ye shall afflict your souls, and offer an offering made by fire unto the LORD.
Joel's call to blow the trumpet, sanctify a fast, and call a solemn assembly invokes the Leviticus 23 solemn-assembly statutes, particularly the Day of Atonement framework with its trumpet, holy convocation, and soul-affliction requirements. The comprehensiveness of the assembly — elders, children, nursing infants — mirrors the Deuteronomy 29 covenant-assembly breadth. Joel deploys the Levitical festival assembly structure as the covenant response framework for a national crisis.
Joel 2:28-29
And it shall come to pass afterward, that I will pour out my spirit upon all flesh; and your sons and your daughters shall prophesy, your old men shall dream dreams, your young men shall see visions: And also upon the servants and upon the handmaids in those days will I pour out my spirit.
Numbers 11:29
And Moses said unto him, Enviest thou for my sake? would God that all the LORD'S people were prophets, and that the LORD would put his spirit upon them!
Joel's Spirit-outpouring promise fulfills Moses' intercession in Numbers 11. When Eldad and Medad prophesied in the camp, Joshua urged Moses to forbid them; Moses responded with the covenant wish that all the LORD's people were prophets with the Spirit upon them. Joel 2:28 records the fulfillment of this Mosaic wish as a divine promise: in the latter days, the Spirit will be poured on all flesh — sons, daughters, servants, handmaids — constitutionally fulfilling the universal-prophecy hope that Moses expressed in Numbers 11.