אִ֣ם ׀ רָחַ֣ץ אֲדֹנָ֗י אֵ֚ת צֹאַ֣ת בְּנוֹת־צִיּ֔וֹן וְאֶת־דְּמֵ֥י יְרוּשָׁלִַ֖ם יָדִ֣יחַ מִקִּרְבָּ֑הּ בְּר֥וּחַ מִשְׁפָּ֖ט וּבְר֥וּחַ בָּעֵֽר׃
when the Lord shall have washed away the filth of the daughters of Zion, and shall have purged the blood of Jerusalem from the midst thereof, by the spirit of judgment, and by the spirit of destruction.
Rashi on Isaiah
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.”
Ibn Ezra on Isaiah
אם For or when.—The remainder will be called holy, when the Lord will have washed away all these from Zion.
Rashi on Isaiah
filth Defilement, as its Aramaic translation; i.e. to say, when He will remove their iniquity through chastening and purging from the world.