This verse is part of the larger story in 2 Kings 10 about Jehu's plot to eradicate the worship of Baal from Israel. Here's a breakdown of its meaning in context:

Context: Jehu has just taken the throne and is pretending to be even more zealous for Baal than Ahab was. He's using deception to lure all the Baal worshipers together.

"He said to him who kept the wardrobe...": Jehu instructs the person in charge of the temple's garments. This implies that the temple of Baal had specific robes or vestments for its priests and worshipers to wear during ceremonies.

"...“Bring out robes for all the worshipers of Baal!”...": Jehu's command is a critical part of his plan. By having the Baal worshipers put on special robes, he accomplishes a few things:

Identification: It clearly identifies who is a worshiper of Baal and who is not. This makes it easier to distinguish them from any Israelites who might be present.
Preparation for Sacrifice (ironically): Robes were often used in religious rituals, giving the impression that a grand ceremony was about to take place. In reality, the "sacrifice" will be the Baal worshipers themselves.
Security (false): The robes might give the worshipers a false sense of security and belonging, making them less suspicious of Jehu's intentions.
Order/control: It allows for greater control of the Baal worshipers because they are wearing a uniform and are no longer simply people in the crowd.

"...So he brought robes out to them.": The keeper of the wardrobe obeys Jehu's command, providing the robes. This shows Jehu's power and authority over the temple of Baal. It also sets the stage for the massacre that follows.

In summary, this verse is a crucial element of Jehu's deceptive strategy to gather and identify all the worshipers of Baal so he can slaughter them. The robes are used as a tool for manipulation and control, leading to their destruction.