http://revach.net/article.php?id=4766

Section:  Avodah   Category: Tshuva
Tshuva - Humdrum Or Haman

In the parsha of Tshuva (Nitzavim 30:2-3) one pasuk says, "V'Shavta Ad Hashem Elokecha", you will return to Hashem.  The next pasuk says, "V'Shav Hashem Elokecha Es Shivuscha", Hashem will return you.  If Klal Yisroel returns by themselves why does Hashem need to return them?

The Imrei Kedesh from Starlisk answers that the gemara Sanhedrin 97b says that if Bnei Yisroel does not do tshuva on their own Hashem will empower a leader as cruel and blood thirsty as Haman to wake us up to do tshuva.

This is the meaning of the two pasukim.  Ideally "V'Shavta", we will recognize the error of our ways without any pressure or threat.  However if our comfortable environment blinds us and makes us deaf to the words of the Torah, then "V'Shav Hashem", Hashem will send a loud and clear message that we can't possibly sleep through.