Why does it discuss laundering the heart?
Radak: Your Teshuvah should not be only visibly, rather, also covertly 1 . This is like it says above (3:10) "Lo Shavah Elai
Malbim: Even when you launder (repent) for appearance, internally you keep thoughts of sin!
Here it says that if they repent, they will be saved. Above (2:22), it says "Ki Im Techabesi ba'Neser v'Sarbi Lach Boris Nichtam Avonech"!
Radak: Refer to 2:22:1:1.
The subject is Yerushalayim, which is feminine. Why does it say "Talin" (masculine)?
Radak: When a verse discusses Keneses Yisrael, sometimes it uses the feminine, for Keneses, and sometimes the masculine, for ha'Am. The same applies when it discusses Yerushalayim. Above it says "Kabsi Lema'an Tivashe'i" (feminine)
What is the meaning of "Talin"?
Radak: It is not staying overnight, rather, constancy. We find like this - "uv'Hamrosam Talan Eini", "ba'Tzavaro Yalin Oz" (Iyov 17:2, 41:14) and similar verses.
Radak citing Targum Yonasan: [Until when] will endure [extortionists among you]?
What is "Onech"?
Rashi: It is your extortion.
Radak: It is Amel (unjust gain) and Aven (evil). The Vov is not pronounced (like a consonant). We find that the Vov in Avlasah is sometimes pronounced, and sometimes not 1 .
I.e. Iyov 5:16 (in our text, the Vov is not even written). In Yechezkel 28:15, Hoshe'a 10:13 and Tehilim 92:16, it is pronounced. (PF)