Our Selichot prayer service revolves around the “thirteen attributes of mercy” which God pronounced to Moshe after the sin of the golden calf. Moshe returned to the top of Mount Sinai after Benei Yisrael worshipped the calf to plead to God on their behalf, and God proclaimed to Moshe the list of His “attributes of mercy,” which we recite repeatedly during Selichot, a service built mainly around these verses.
The source for this practice is the Gemara’s remark in Masekhet Rosh Hashanah (17b) that at the time when God proclaimed the thirteen attributes, He “wrapped Himself as the leader of the congregation and showed Moshe the arrangement of the prayer. He said to him: Whenever Israel sins, they shall perform this arrangement before Me, and I will forgive them.” The Gemara here teaches that God Himself established this procedure of reciting the thirteen attributes in order to earn forgiveness and atonement.
Much has been written about the precise meaning of this passage, and how we earn expiation for our sins by performing this service. Leaving this question aside, it is also noteworthy that the Gemara depicts God as actually leading the service. He did not just instruct Moshe to teach Benei Yisrael to perform this service, but modeled it for us, by appearing as a chazan in the synagogue leading the prayers.
Rav Yehuda Amital suggested that the meaning of this image is that as we pray to the Almighty, He in a sense participates in the prayers with us. We introduce our Selichot service by reciting a long series of verses (beginning with “Shomei’a tefila adekha kol basar yavo’u”) that speak of God’s unlimited power and authority. A prerequisite to Selichot, to expressing remorse and begging for forgiveness, is to recognize God’s absolute control and authority over us and the universe, so we understand the full extent of the magnitude of the audacity and betrayal that sinning involves. However, these thoughts can leave us feeling too distant from God to turn to Him in prayer. The more we focus on God’s transcendence, the more difficult it is to experience immanence. Reflecting on His infinite power creates a vast gulf between us and Him that could discourage us from speaking to Him. And so the Gemara depicts God as a sheli’ach tzibur praying along with us. Chazal here seek to remind us that God takes interest in us, and He even joins us in our lowest moments, when we have betrayed Him and humbly seek forgiveness. He is not distant, but is standing, as it were, alongside us, accompanying us when we feel broken and vulnerable, eagerly anticipating our repentance and intently listening to our heartfelt prayers.