The “sacred assembly” was called to return to God and rend their hearts.  They were called to return by calling a fast.

“Declare a holy fast; call a sacred assembly. Summon the elders and all who live in the land to the house of the Lord your God and cry out to the Lord... Gather the people, consecrate the assembly; bring together the elders, gather the children, those nursing at the breast.” (1:14; 2:15-16) 

“’Even now,’ declares the Lord, ‘return to me with all your heart, with fasting and weeping and mourning.” (2:12) 

When people fast and pray they rend their clothes as an external sign of repentance. But God called the people to rend their hearts instead—a call to match their external expression with internal consecration. 

“Rend your heart and not your garments. Return to the Lord your God, for he is gracious and compassionate, slow to anger and abounding in love, and he relents from sending calamity.” (2:13)

God, ever so gracious and compassionate, slow to anger and abounding in love, relented from His judgment when the leaders led the people to fast and pray.

As a result, God turned the wailing to rejoicing (1:5, 11a; 2:21), ruining of fields to greening of pastures (1:10a-b, 11b; 2:22a), destroying of grains to filling of the threshing floor (1:10c; 2:24a), drying up to dripping of new wine (1:10d; 3:18), failing of oil to overflowing of vats (1:10e; 2:24b), withering of trees to bearing of fruits (1:12; 2:22b) , and cutting off of food to providing an abundance (1:16; 2:26).

In the end, the people drew closer to God. “Then you will know that I am in Israel, that I am the Lord your God and that there is no other; never again will my people be shamed.” (2:27) “Then you will know that I, the Lord your God, dwell in Zion, my holy hill.” (3:17)

Amazing what God can do if we return and rend our hearts! He can turn things around for us to know Him more.