Joel wanted the temple priests, the minister of Yahweh, to deliver a prayer to Yahweh between the altar and the vestibule, in the open court. They were to weep and ask God to spare them. They did not want the heritage of Yahweh to be a mockery or a byword among the various countries. There should never be a question about their God. Yahweh should show himself during this time of the locust plagues.
In an interesting bit of irony, this author points out that the foreign temples have a lot of security, as if the temples were in prison. These temples are like someone who has offended a king. They have gates on all sides of them, as if they are awaiting a death sentence. Their temple priests have secured their temples with doors, locks, and bars because they are afraid that robbers will come into the temple and steal things from it. They have so much light in the temple for themselves, rather than for their gods who cannot see anything anyway, with or without light.