Why does it say "Ratzisa Hashem Artzecha"?
Rashi: If You will return the captivity of Yakov, and bear their sin, and cover their Chata'im, and cease Your anger from them (verses 2-4), then You desired Your land and Your world is conciliated. As long as You do not do so, Your land and world are not appeased.
Radak: Just like You were appeased in Bayis Sheni, and bore their sin, covered their Chata'im and ceased all Your anger, so return us now from this Galus. Just like You were angry at us all these years, now desire us!
Malbim: This is one of three ways that Hashem was appeased with His nation - He was appeased with his destroyed land. Also refer to 85:2:2:3, 85:3:1:2. It mentions Shem Havayah, for this was not based on Midas ha'Din, rather, Midas ha'Rachamim; He had mercy on its desolation. However, after the mercy passes, He could get angry again. Had the salvation been based on Din, it would be permanent 1 . The final redemption will be permanent, and Hashem's Midah of anger will totally cease - "uv'Chesed Olam Richamtich", "Boshes Alumayich Tishkachi" (Yeshayah 54:8, 4).
Presumably, he means as long as there is no change in their deeds. Even if they merited based on Din, if later they soured, the desolation could return! (PF)
What is the meaning of "Shavta Shevus Yakov"?
Radak #1: "Shavta" is Po'el Yotzei (it acts on others), as if it said Hashivosa.
Radak #2: Shavta is Po'el Yotzei, from a root regarding rest, like "Shuvah Hashem Rivevos Alfei Yisrael" (Bamidbar 10:36), "v'Shav Hashem Es Shevusecha" (Devarim 30:3), "Shuvenu" (below, verse 5); He should give respite from the affliction of Galus. R. Yehudah Chiyug holds like this.
Malbim: This is the second way that Hashem was appeased with His nation - He returned them from captivity.
Why is it written Shevis, and we pronounce it Shevus?
Radak: These are the same.
Malbim: The Kesiv hints that they were still captive; they were under the Reshus of Malchei Pras. This Ge'ulah came via request from Koresh and with his permission; it is attributed to Yisrael. This shows that it is not the true Ge'ulah that Hashem promised, which will be complete, from Hashem, with wonders.
