Ashkenazic custom, as established by the Rama (O.C. 581:1), is to begin the Selichot recitation on Motzaei Shabbat – either the Motzaei Shabbat immediately preceding Rosh Hashanah, or, if Rosh Hashanah falls early in the week, then the Motzaei Shabbat of the previous week. The significance of beginning the daily Selichot recitation specifically on Motzaei Shabbat is reflected in the “Be-motzaei Menucha” hymn chanted during the first Selichot service, which begins, “Be-motzaei menucha kidamnukha techila” – “After the [day of] rest, we have begun to approach You [to beg for forgiveness].” As many have noted, there seems to be special importance to beginning the Selichot period, when we ask for forgiveness in preparation for Rosh Hashanah (and then in the days leading to Yom Kippur), specifically on Motzaei Shabbat, after observing Shabbat.
One explanation that has been suggested is that we begin Selichot after Shabbat because our minds have been cleared of our mundane concerns. Shabbat, which is famously described as “me’ein olam ha-ba” – an experience bearing some resemblance to life in the next world – is intended to be a time of complete contentment, free of anxiety, dissatisfaction and displeasure. Just as God completed the process of creation after six days, we, too, are to consider our workweek “creation,” our efforts to build, produce and earn a livelihood, complete when Shabbat begins. On Shabbat, we are to feel perfectly content with everything we have, and rid our minds of the worries and concerns that occupy us and drive us to work hard for a living during the workweek. The Shabbat experience should be one of serenity and repose, when we feel at ease with all we have, and can enjoy the many blessings we’ve received without worrying about what we need to do in order to obtain more.
It is perhaps for this reason that we begin Selichot specifically after Shabbat. If we would begin Selichot during the workweek, when our minds are filled with the normal pressures and anxieties surrounding our efforts to secure a livelihood, our thoughts and feelings during the Selichot prayers would likely revolve around those pressures and anxieties. We would reduce Selichot to nothing more than a chance to beg God for assistance in solving our personal problems and satisfying our material desires. By beginning Selichot after Shabbat, we are able to approach Selichot from a loftier mindset. After focusing throughout Shabbat on our joy, gratitude and contentment over our blessings, we can enter the Selichot period with higher, more meaningful goals. Emotionally unencumbered by our mundane anxieties, we can focus on our desire to enhance our relationship with our Creator, and our wish that God’s Kingship be recognized throughout the world (one of the primary themes of the Rosh Hashanah liturgy). Specifically after experiencing the special joy and serenity of Shabbat, we are in a position to enter Selichot with higher goals and aspirations, seeking not only the fulfillment of our relatively trivial personal requests, but also the realization of our spiritual ambitions for both ourselves and the world generally.
(Based on Rav Yaakov Glick’s Ekhsof Noam Shabbat, p. 12)