ישעיהו ד:ד פירוש: רש״י ואבן עזרא

When the Lord shall have washed away Heb. אִם [usually “if.”] When the Lord shall have washed away. There are instances of אִם being used in this manner in the usage of כִּי ; and so (Job 8:18): “But when (אִם) men destroy him from his place,” is [equivalent to] כִּי יְבַלְּעֶנּוּ. Also (Gen. 24:9): “Until when (אִם) they will have finished drinking.”

אם For or when.—The remainder will be called holy, when the Lord will have washed away all these from Zion.

filth Defilement, as its Aramaic translation; i.e. to say, when He will remove their iniquity through chastening and purging from the world.