Q: This article was originally written as a response to a couple that wrote expressing concern over the spiritual implications of recurring problems with their mezuzot and his tefillin. Each time a scribe checked them, something invalid was found, and even though they immediately would have it corrected, a new problem would be discovered the next time that hadn't appeared or been noticed previously.
A: A person's possessions are affected by his current spiritual state. We know from the Talmud and other sources that one of a Jew's purposes is to rectify his possessions, and the great sages were also very respectful and careful with their, (and of course, others'), possessions.
Furthermore, the term used in the Shema (a compilation of three Biblical passages (Deuteronomy 6:4-9, 11:13-21, Numbers 15:37-41) beginning with this word, which we are commanded to recite twice daily) for "possessions" is me'odecha, "your might," which inChassidut is explained to also mean the transcendent, makif, states of the soul. These superconscious (i.e. as yet unconscious) states in one's soul-root can descend and manifest themselves into one's possessions. In other words, what's going on with one's possessions can reflect what's going on in one's soul-root before the person is even aware of it himself.
This is seen in the laws of tzara'at, the "leprous" plagues that people used to get. The Rambam explains that these plagues would first appear on one's house, (in which is manifest the "distant transcendent state" makif harachok, of the soul). If he didn't improve his behavior, they would appear on his clothes, (the "close transcendent state" makif hakarov). Only if he still didn't improve his behavior would they finally appear on his skin.
Now, tefillin and mezuzot are one's most holy and representative possessions. They are both related to the house, since the compartments of the tefillin are called batim, ("houses"), and the mezuzah signifies that the house and all its contents are holy and dedicated to G-d. More specifically, the mezuzah reflects the "distant transcendent state" of one's soul, and the tefillin, being something that is worn, reflect the "close transcendent" state of the soul. In terms of levels of the soul, mezuzah reflects the yechidah, (the higher of the two transcendent soul-states), and tefillin the chayah.
Thus, if there is some defect in one's tefillin and/or mezuzot, it means that there is some subtle imbalance in his superconscious soul-powers. This "defect" may or may not have yet affected the conscious part of the soul. If not, and it is corrected in the tefillin/mezuzot, it can be "caught" before it enters consciousness.
Where do all these soul-imperfections come from? The fact that one has them (as manifest in his tefillin/mezuzot) does not necessarily mean that he is such a bad or evil person. It may simply mean that he is spiritually active. When one is experiencing and exploring new levels of spirituality, he inevitably encounters admixtures of impurities in his personal interpretation of what he is experiencing. These impurities must be expelled, just as when one eats even the purest food, there are parts of it that cannot be assimilated and must get excreted.
The more spiritual changes one undergoes, the more impurities will be expelled. It doesn't mean that things are bad, just that things are happening.
Thus we find that many tzadikim check or even change their tefillin/mezuzot often. The Lubavitcher Rebbe, for example, frequently advised people to check theirs, often with astonishing results.