2. This week we will IY"H start saying slichos. The S.A. paskens that if you are not davening with a minyan then you cannot recite the 13 midos ha'rachamim. The Rishonim already question why this should be so. The Mishna in Megillah (23b) lists those things which require a minyan, and conspicuously absent from the list is the recitation of the 13 midos. The midos are, after all, just a tefilah, a bakashas rachamim -- why should they be categorized as a davar she'b'kedusha that requires a minyan? What is the source for such a din?
Some point to the gemara in Rosh haShana (17b) that says that Hashem wrapped himself in a talis like a shliach tzibur and taught Moshe the 13 midos as the source. Since the gemara refers to Hashem acting as shliach tzibur, it implies that a tzibur is needed. As to why this din is left off the list in the Mishna in Megillah, it could be that the Mishna there is listing chiyuvim. There is no chiyuv to recite the 13 midos -- if you choose to take advantage of their power and add them to your tefilah, then you need a minyan to do so.
The Maor vaShemesh (end of Parshas vaYechi) suggests another hesber. The gemara writes that Hashem told Moshe that whenever Klal Yisrael sins "ya'asu lifanei ka'seder ha'zeh," of the 13 midos, "V'ani mochel lahem." The Rishonim point out that the gemara does not say "kol ha'omer" -- whoever recites the 13 midos. It says "kol ha'oseh" -- whoever does the 13 midos. A person must put those behaviors of rachum, chanun, erech apayim, etc. into practice and live them to benefit from them and be granted mechilah. (I can't help but think that in the back of the Maor va'Shemesh's mind was the RaMaK's sefer Tomer Devorah, which is devoted to explaining how to put Hashem's midos ha'rachamim as described in the pasuk "Mi K-l kamocha nosei avon..." into practice. "Mah hu -- af atah" -- we have a concept of imitation Dei. If G-d reveals to us that he acts with certain attributes of mercy, it obligates us to behave in a similar fashion.)
It's impossible for any one individual, says the Maor va'Shemesh, to truly embody all of the 13 midos. Each one of us has personality quirks that tilt us in the direction of one midah or another. It's only when we join together as a tzibur and blend all our individual talents together that we can cover all 13 bases.
Coming back to Rav Ruderman's idea, the tikun of bein adam l'chaveiro is perhaps even more necessary at this time of year because it is what enables us to truly come together as a community so that we can fulfill the 13 midos and merit receiving the bracha of "kol ha'oseh... ani mochel lahem."
3. Lastly, just to put you in the right mood: