Of all the vessels of the Beit Hamikdash, the ארון הקודש, the holy ark, is the most prominent and holy. It was from above the כרובים, Cherubs, that Hashem communicated with his prophets and High Priests.
The Torah says, ועשו ארון, “And They shall make the ארון.” It should have said, “And You shall make the ארון.” The reason for the “they” was so that all of Israel will have a share in its construction. All were to benefit from the light that emanated from it.
The ארון was also the symbol of purity, honesty, and integrity. It was meant to teach the importance of being upright in how we conduct our affairs. We were not supposed to be אחד בפה ואחד בלב, one way with our mouth and another with our heart.
This is why the ארון had gold on the inside and on the outside. Holiness does not tolerate שקר, falsehood. To achieve holiness, one needed to be clean in thought and deed. This was what the ארון קודש symbolized.