Food For The Soul
...The above also enables us to understand a statement of the AriZal  that a person who is careful not to eat even the slightest amount of chametz on Pesach can be certain that he will not sin throughout the entire year to come.
On the surface, this statement is problematic.
Man has been given free choice and has the potential to determine his path of conduct. How is it possible to say that his taking care not to eat chametz for eight days will cause free choice to be taken away from him?
The resolution is that the AriZal is speaking about sins committed unknowingly.
Although a person did not partake of chametz on Pesach, it is possible that he will willfully perform a transgression, because he retains his free choice. He will not, however, perform a transgression unknowingly (that much). For his precaution not to eat chametz will affect his inner nature, endowing it with a tendency toward holiness.  As a result, he will not be subconsciously drawn to sin. 
- (Back to text) Cited by the Baer Heitev, Orach Chayim 447:1; see also Zohar, Vol. III, p. 282b.
- (Back to text) This applies to a benoni, not only a tzaddik.
Although as Tanya (ch. 29) states, in the benoni, "the vital soul (the animal soul) is the person himself," nevertheless, by nature, the animal soul enclothed within Jews is from kelipas nogah, the level of kelipah that shares a connection with good. Thus it desires only material entities which are permitted. (It is, however, through indulging one's desires for permitted things that one establishes a connection between one's animal soul and the three impure kelipos, which are the source of evil.)
- (Back to text) On this basis, we can understand why the promise that a person will not sin is made with regard to precautions against partaking of chametz.
Matzah reflects bittul and faith and thus leads to the observance of all of the 613 commandments (see Tanya, ch. 33). Chametz, the opposite of matzah, reflects self- concern and pride which leads to all forms of evil.