http://revach.net/article.php?id=4494

Section: Parshas HaShavua   Category: Quick Vort
Parshas Shemini: Shem MiShmuel & Gerrer Rebbe - After Pesach Tshuvah Starts In The Belly
Most years the Shabbos immediately following Pesach we read Parshas Shemini.  The Shem MiShmuel says that this is no coincidence.  Matza is called Nahama D'Asvasa the healing bread and Nahama D'Mihemnusa the bread of faith.  On Pesach we take refuge under the Kanfei HaShechina and renew ourselves as the Am Hashem.  Therefore immediately after Pesach when we go back to regular food, the Torah warns us that all year round we must avoid eating unkosher foods which are discussed in Parshas Shemini.

The Bais Yisroel of Gur says that when a person is on the road to tshuva and cannot suddenly take on everything all at once, it is especially important for him to take on carefully keeping Kashrus.  By eating non-kosher food he is being Mitamtem Es HaLev, closing the heart and impeding his progress.  By eating kosher food only, he is paving himself a smooth road along which to travel towards his ultimate goal.