Does God care more about the intentions of a person doing a mitzvah, or that the rules are followed to the letter? For example: one puts up a mezuzah and later discovers that it was missing a letter and therefore not kosher. Which is more important: that the person intended and tried to fulfill a mitzvah or that the mitzvah was actually performed in the correct manner? For the record, I believe God cares about intentions, but I am interested in the rabbinical perspective. Thank you.
What a fascinating question! The answer is that they are both important — it is important that a person should try to fulfill a mitzvah in the correct way, and it is also important that the person in fact succeeds in doing so.
You are certainly correct in your belief that God cares about intentions. That is what I understand you to be asking. Not only is the result in succeeding to fulfill a mitzvah important, but there is definitely great value and reward for thinking and trying to fulfill a mitzvah even if one is not ultimately successful due to circumstances beyond his control.
Our Talmudic rabbis teach (based on a verse in the Book of the Prophet Malachi 3:16): Rav Asi said, “Even if a person just thought to do a mitzvah, but was prevented from doing so, he receives reward as if he had in fact fulfilled the mitzvah.” This statement clearly teaches that God rewards good intentions to do a mitzvah, as much, or nearly as much, as if the person actually succeeded in fulfilling the mitzvah. In fact, we are also taught that, “A good intention is combined with a good deed” — meaning that a person receives reward for both his good intention and his good deed.
God know we are only human and can do only so much. Although we are expected to try our best, sometimes “outside forces” come into play to decide whether a person succeeds in fulfilling a sincere thought to do a mitzvah.
However, ultimately it is the ideal that a person succeed in fulfilling a mitzvah, although he will certainly receive great reward for intending and trying to fulfill a mitzvah even without “success”. Therefore, in the event the mezuzah is found to be not kosher, such as in the case you asked about, the person should buy a kosher mezuzah to replace it (and get his money back for the non-kosher one!).