In this week's Parsha, the Torah describes the dimensions and other details involved in the construction of the Aron (שמות כ"ה:י'-ט"ז). The Torah then says that in the Aron were to be placed the Luchos, the "testimonial tablets" which contained the Aseres HaDibros (שם פסוק ט"ז). According to some commentators, a copy of the Sefer Torah was eventually placed into the Aron as well.
The Gemara in Yoma (דף כ"א.) teaches that the place where the Aron rested was not included in the measurements of the Beis HaMikdash, meaning that somehow, the Aron did not take up any space. This was obviously some sort of miracle. The idea seems to be that because the Aron was so spiritual, it didn't occupy any physical space. One would think, however, that since the Aron was made just to hold the Luchos and the Torah, that they also would not take up any space in the Aron or that instead of the Aron taking up no space, it would be the Luchos and the Torah which would take up no space. Yet Chazal say that they filled the Aron to the max. The question then arises as to why it was only concerning the Aron, and not the Luchos and the Torah, that this miracle of not taking up any physical space was performed.
Rav Moshe Feinstein comments that each Jew should strive to be as holy as the Aron and fill himself with Torah, just as the Aron was filled with Torah. This Torah, however, must "take up space" within the person, who becomes like a living Aron. The Torah must be part of his every move and thought. If a person doesn't learn to his fullest ability, there is an empty space in his personal Aron; there is something missing. But if one does learn to his fullest ability, and the Torah does indeed "fill him," he should then make himself humble, as if he doesn't occupy any space in this world, just like the Aron occupied no space in the world. This perhaps is the message of the miracle which impacted the Aron, but not the Luchos and the Torah. A person should realize that since his essence is entirely spiritual, he therefore should have no connection with the dimensions of the physical world.