Shabbat Shuva (not “Shabbat Teshuva”) is named after the Haftarah from Hoshea that begins with the words, “Shuva Yisrael”. It comes out on either VaYelech or He’ezinu. In addition to Hoshea, we also read a few verses from Michah, and half a chapter of Yoel.
It connects to He’ezinu through the theme of dew. G-d’s love for the Jewish People is compared to dew, which unlike rain, never fails, and nurtures the land every day regardless of circumstances. The difference between Tal (dew) and Matar (rain), unconditional and conditional love, can tell us a great deal about our relationship with G-d.
The connection to VaYelech is similar, but with a twist: The Illogic of Teshuva