The ward of their God, i.e. that ward, or charge, or business which God had prescribed to them. And the ward of the purification; and in particular the charge of purification, i.e. of taking care that no unclean person or thing might enter into the house or courts of the Lord; which care did certainly belong to the porters, as is expressed, 2 Chronicles 23:19, and at this time, and in some sort, as it seems to the singers, who, besides their proper employment, were also over the business of the house of God, as is affirmed, Nehemiah 11:22; which being a general expression, may well comprehend, if it doth not principally design this, that they should take care to keep the house of God free from all pollution. And possibly as the porters were to take care that no unclean thing might enter there, so if it should through their inadvertency enter in, the singers were to remove it.
Related Commentaries of Nehemiah 12:45
Nehemiah 12:45
45 And both the singers and the porters kept the ward of their God, and the ward of the purification, according to the commandment of David, and of Solomon his son.