Then the priest shall command that they wash [the thing]
wherein the plague [is]
The priest did not wash it himself, but ordered others to do it; and this was either the part in which the plague was, or the whole garment or skin in which it was; which may be typical of the washing of the garments of men in the blood of Christ, which cleanses from all sin, ( Revelation 7:14 ) ( 1 John 1:7 ) ( Zechariah 13:1 ) : and he shall shut it up seven days more:
the garment or skin in which the leprosy was, or suspected to be, to see what alteration would be made by that time through the washing, whether the colour would be altered, or whether it would spread any more or not.