Ibn Ezra on Exodus 30:21/אבן עזרא על שמות ל׳:כ״א

1ורחצו (And they shall wash) - He reiterated and mentioned it another time [he had already written so in verse 19], to instruct that they should do so always [for future generations]. Or, he mentioned this [to add a punishment to the warning, to indicate] that if they do not do so, they are liable to death [as it is stated 'and they shall not die'; and so Rashi explains].