It will be helpful to begin a new sentence here (so Good News Bible). This verse describes part of the preparations for the Passover.

Having placed the priests according to their divisions means Josiah divided the priests into their regular groups, or teams, for serving in the Temple. So we may translate “Josiah assigned each of the priests to serve according to their particular order.” The priests were the men who received authority from God to offer sacrifices and perform other religious ceremonies on behalf of his people. They served as intermediaries between God and the people of Israel. In the Old Testament the office of the priesthood was limited to the tribe of Levi, and more specifically to one family of that tribe, the family of Aaron. Regulations with regard to the qualifications of priests are given in Lev 21.16-23. The word priest is often rendered “sacrifice-making person” or “ceremony person.”

Arrayed in their garments refers to the priestly garments (see Exo 28). The clothes included a number of objects and layers. When the priests were so dressed, they were ready for service. This phrase does not say that they were simply wearing clothes, so “proper priestly clothes” (Contemporary English Version) is better than “priestly robes” (Good News Bible).

In the temple of the Lord may be rendered simply “in the Temple” (Good News Bible).

Here is an alternative model for this verse:

• He [or, Josiah] saw to it [or, made sure] that the priests were in the Temple, ready for service. He made sure that each one was properly dressed, and standing with his assigned group.

Quoted with permission from Bullard, Roger A. and Hatton, Howard A. A Handbook on 1-2 Esdras. (UBS Helps for Translators). Miami: UBS, 2019. For this and other handbooks for translators see here.