While every transgression carries some sort of repercussion, some are more severe than others. Regarding one who eats chametz on Pesach, the Torah tells us, "Seven days sourdough should not be found in your houses, for anyone who eats leavened bread will be cut off from the Jewish nation" (Shemos 12, 19).One who is guilty of this transgression has severed his spiritual connection to Bnei Yisrael.
Rav Wolbe (Shiurei Chumash) elaborates on this concept. Physical existence is dependent on a specific set of conditions. One cannot survive if he deprives himself of food, drink or sleep. Similarly, spiritual existence is only possible when certain conditions are present. These conditions are the mitzvos. One, who fails to put on tefillin or sit in a sukkah, has not merely passed up an invaluable opportunity; he has caused himself to be lacking an integral part of his spiritual makeup. Every mitzvah can be compared to a limb in the spiritual body. The lack of a limb is a handicap which inhibits proper spiritual existence.
Refraining from eating chametz on Pesach is so vital, that one who fails to do so has, so to speak, caused a system failure. He has not properly provided for his spiritual body, and in its present state it can no longer survive. In the words of the Torah, he has been cut off from Bnei Yisrael.
While certain mitzvos are critical, all mitzvos are necessary. Many people have predispositions to specific mitzvos. Some love learning while others enjoy performing chesed. For some Shabbos is in their blood while others connect with mitzvos performed during the Yomim Tovim. However, all mitzvos are imperative and they must all be performed to ensure a healthy spiritual existence. And the same applies with regard to refraining from transgressions. Some aveiros are easier to abstain from and others are harder to abstain from, but the effort must be made to refrain from them all. Performance of all the mitzvos of the Torah is the key to spiritual well being!