The word of the LORD that came to Joel, the son of Pethuel:
...
    Put on sackcloth and lament, O priests;
wail, O ministers of the altar.
Go in, pass the night in sackcloth,
O ministers of my God!
Because grain offering and drink offering
are withheld from the house of your God.
    Consecrate a fast;
call a solemn assembly.
Gather the elders
and all the inhabitants of the land
to the house of the LORD your God,
and cry out to the LORD.
    Alas for the day!
For the day of the LORD is near,
and as destruction from the Almighty it comes.

Joel 1:1,13-15 (ESV)

Joel warns the LORD's people of impending judgment ("Alas for the day! For the day of the LORD is near... ") and exhorts them to collective repentance over their spiritual barrenness, described in the preceding and following verses, that leaves them without an acceptable sacrifice of praise - "grain offering and drink offering are withheld from the house of your God."

Culturally, we tend to think of sin as individual culpability and so repentance as an exclusively individual practice. But individual sin is the business of the entire church. Failure to promote the purity of the church is disregard for the Lord's command to shepherd His sheep and neglect of the Elders' vow. Failure to exercise church discipline over sin is a more egregious neglect of the Elders' vow and a form of complicity.

There are lessons on the corporate repentance of God's people to be learned from these verses:
- it should be displayed and initiated by the spiritual leadership of the congregation
Put on sackcloth and lament, O priests;
wail, O ministers of the altar.
...
Gather the elders...
- it should not be accompanied by a credible demonstration of remorse over sin
Go in, pass the night in sackcloth
...
    Consecrate a fast
...
and cry out to the LORD.
- it should involve the entire congregation of those who have committed public sin
call a solemn assembly.
Gather... all the inhabitants of the land
to the house of the LORD your God...

if my people who are called by my name humble themselves, and pray and seek my face and turn from their wicked ways, then I will hear from heaven and will forgive their sin and heal their land.   2 Chronicles 7:14 (ESV)

Amen. Come, Lord Jesus.