The Talmud teaches that the Ark contained both the broken remnants of the first set of Luchos and the complete and unbroken second Luchos.
The first Luchos were given to Moshe immediately after the revelation at Sinai, before Bnei Yisrael sinned and worshipped the Golden Calf. At that point, they were spiritually perfect; thus, the remnants of the first Luchos represent the tzaddik—the Jew in his most perfect and elevated state.
The second set of Luchos were given to Moshe on Yom Kippur, after G‑d pardoned Bnei Yisrael for the sin of the Golden Calf. These Luchos represent the baal teshuvah—a person who may have strayed from the Torah’s ways in the past, but has since repented.
Both the tzaddik and the baal teshuvah were thus represented in the Aron, by the first and second Luchos, respectively. There is, however, a third possible state in which a Jew may find himself: having transgressed the Torah but not yet made amends. The first Luchos, the Luchos of flawlessness, no longer represent him. The second Luchos, the Luchos of repentance, do not yet represent him either. But this Jew, too, is represented in the Aron—by the broken state of the first Luchos.
By representing all three categories of Jews in the Aron, the Torah highlights that the commandment to build a Mishkan—and likewise, the eternal lesson we learn from this mitzvah—applies to every Jew equally. Regardless of your current spiritual state, whether perfect or far from it, you must endeavor to elevate your material life to serve exclusively as a home for G‑d.
—Likkutei Sichos, vol. 6, pp. 156–157
