We spoke about "adopting a mitzvah" - about choosing one mitzvah which you'll first learn about, prepare for and (to the best of our ability) commit to trying very hard to keep it no matter what stands in the way and no matter how embarrassing it might get.
Let's first look at mitzvos in general. The Mesilas Yesharim writes that we're in this world to develop specific personality qualities. We'll need these qualities to fully enjoy the warm closeness of the Divine Presence in the next world (because even without sins, an unrefined, coarse soul will simply be unable to enjoy God's closeness just as the inability to read will prevent the enjoyment of a book). The tools for creating these qualities, writes Rabbi Luzzato, are the mitzvos of the Torah. Now, obviously, each mitzvah has to deeply affect us - change us - or else what difference will it make?
As an example, let's try mezuza. How can mezuza make us different (besides changing the shape of your thumb upon being struck by the hammer while putting one up)?
I think it's obvious that the real mitzvah of mezuza only begins with the last hammer blow (or application of two-sided tape). Of course it's worthwhile ensuring that your mezuzos are kosher (and properly attached), but even that's only an introduction, a means to an end. So what's it really all about?
Every time you walk into or out of your house or room, you have an opportunity to think about what's written there (the first two paragraphs of Shema, by the way) and how it can influence you deep inside: the message includes the ideas that there's one God, He's all powerful, we must love Him and serve him with all our hearts and soul, etc., etc., etc.
But isn't all of that already included in the separate mitzvah of the Shema: what's special about a mezuza? I think we should examine the way this message is delivered.
Here's what R' S.R. Hirsch (Deut. 6; 9) says. When we think about a mezuza (especially, from time to time, as we walk past one) we should think of the way it was created. It must be written l'shma, that is, while the scribe is fully conscious of the words' meanings - his entire concentration is focused on nothing else. It must be written by someone who is personally obligated in the mitzvah (not as some theoretical exercise, but out of personal conviction). The production of the mezuza (as with all mitzvah objects) must be as attractive as possible. In addition to that, a mezuza requires "kesiva tama" - an added level of accuracy and perfection so that, for instance, all the letters are clearly formed and none overlaps its neighbor.
Why? What difference does it all make? Can't it be read in any case (and who's going to actually read a mezuza anyway)?
Here's how R' Hirsch answers (paraphrased). When we think about the high level of concentrated effort required to transmit the messages contained in a mezuza, we should realize that we must similarly commit ourselves to intelligently absorbing these ideals. Not as a mindless automaton or with half a heart, but with minds and feelings fired by the same sense of intense devotion and precision with which the mezuza was first created.
Mezuza, then, is the manner by which we are to carry out those ideals taught by the Shema.
But isn't the mezuza really there to protect our homes and health? Ok. Perhaps it does that too, but it's not the main point.
If it were all about protection, we'd probably have been told to wear mezuzos on our bodies (as a kind of amulet). Instead, observes R' Hirsch, they're placed on our buildings. But not on all of our buildings: only on those within which we're active (as opposed to empty, unused space) and which are fully usable as homes (as opposed to undersized or roofless rooms).
This suggests that it's not the space - the property - that is to be the subject of this mitzvah, but the normal home and work activities taking place inside. From the moment we first approach the threshold of our homes, we are, therefore, to try to infuse full enthusiasm and loving devotion before God into our eating and sleeping, our working and playing, the way we interact with our families, indeed, into every conscious moment.
Pause and think this way upon passing a mezuza even once a day, and see if you don't gradually change the very tone of your Divine service!