It is not aimed at rejecting heretical beliefs but rather at affirming religious convictions and strengthening the Israelites' bond with God. Only after Israel begins performing God's commandments can they be redeemed. Torah is not satisfied with people abstaining from wrongdoing. It demands positive affirmative action. I believe the common denominator between these two commandments is that they are both expressions of belonging to the Jewish people.
Circumcision is an initiation into the Jewish people.
It is a sign of the covenant between God and the descendants of Abraham and inducts the newborn baby into this covenantal relationship with God. The Paschal lamb is also an expression of belonging. However, unlike circumcision which relates to the individual baby, the Paschal lamb is a family-centered act. Partaking in the feast of the Paschal lamb is an expression of belonging to the family, of one's connection to the home. It is the Jewish home, the family, which is the core of Jewish existence.