“And you shall place into the ark …” (25:16)
The Sages (Yoma 21a) relate that the Ark was not included in the measurements of the Beis HaMikdash; because of its spiritual nature, it did not occupy physical space. Now if this miracle was done for the Ark, which functioned solely as a repository for the Torah and the Luchos (Tablets), we would think that the Torah and the Tablets themselves, with their much greater degree of sanctity, should have been all the more worthy of such a miracle.
Yet the Sages say (Bava Basra 14a) that the Torah and the Tablets filled the Ark to capacity, calculating their measurements in detail to establish exactly how the space in the Ark was totally occupied. Why, then, was this miracle done only for the Ark but not for the Torah and the Tablets?
We see from here a lesson that applies to all of us: Each Jew must endeavor to make himself like the Holy Ark and to fill himself completely with Torah. Therefore, if he does not learn to the utmost of his capability, he will leave an empty space in his personal “Ark,” which should have contained the entire Torah.
Once he has learned to his capacity, however, he must strive to make himself humble as if he does not occupy any space in the world, and he should realize that since his essence is entirely spiritual and therefore has no connection with the dimensions of the physical world. (Darash Moshe, Hagan HaRav Moshe Feinstein zt”l)