Chronicles II 35:15

15 And the sons of Asaph the psalm-singers at their post according to the commands of David, and Asaph, and Aeman, and Idithom, the prophets of the king: also, the chiefs and the porters of the several gates; —it was not for them to stir from the service of the holy things, for their brethren the Levites prepared for them.

Chronicles II 35:15 Meaning and Commentary

2 Chronicles 35:15

And the singers the sons of Asaph were in their place
In the court of the priests, singing and playing on their instruments while the sacrifices were offering:

according to the commandment of David, and Asaph, and Heman, and
Jeduthun the king's seer;
the same with Ethan; and everyone were seers, as Jarchi interprets it, that is, the three last:

and the porters waited at every gate;
such of the Levites as were in, that post and office:

they might not depart from their service;
to let people in and out, that came for their passover lamb, and share in their other offerings:

for their brethren the Levites prepared for them;
because they were not at leisure to prepare for themselves.

Chronicles II 35:15 In-Context

13 And thus till the morning. And they roasted the passover with fire according to the ordinance; and boiled the holy in copper vessels and caldrons, and went on well, and they quickly served all the children of the people.
14 And after they had prepared for themselves and for the priests, for the priests in offering the whole-burnt-offerings and the fat until night, then the Levites prepared for themselves, and for their brethren the sons of Aaron.
15 And the sons of Asaph the psalm-singers at their post according to the commands of David, and Asaph, and Aeman, and Idithom, the prophets of the king: also, the chiefs and the porters of the several gates; —it was not for them to stir from the service of the holy things, for their brethren the Levites prepared for them.
16 So all the service of the Lord was duly ordered and prepared in that day, for keeping the passover, and offering the whole-burnt-sacrifices on the altar of the Lord, according to the command of king Josias.
17 And the children of Israel that were present kept the passover at that time, and the feast of unleavened bread seven days.

The Brenton translation of the Septuagint is in the public domain.