In Parashat Vayehi, Ya’akov Avinu tells Yosef that he vanquished the Emorites with his sword and with his bow (Bereshit 48:22). Onkelos translates “sword” as “prayer”, and “bow” as “supplication”, to teach us that Ya’akov used the power of Tefila to overcome his adversaries. From this, the Brikser Rav says that there are two types of prayer; the first kind is the prayer that was instituted and standardized by the Anshe Knesset HaGedola, like the Amida. This kind of prayer is comparable to a sword because, just as a sword is sharp and needs minimal effort to inflict damage, so too is the Amida effective even with less-than-ideal concentration. On the other hand, supplications such as the Selihot prayers are compared to a bow and arrow; the more one pulls the bow’s string, the further the arrow will travel. This is especially true with the Thirteen Middot which are said multiple times during the Selihot and Yom Kippur as well.
Regarding the Thirteen Middot (“Hashem, Hashem, E-l Rahum Vehanun…”), it should be noted that they should be recited only with a Minyan. However, if one is simply reading them as though he were reading any other verse from the Torah with cantillation, this is permitted (Shulhan Aruch, O.H 565:5).
Summary: One should concentrate properly when reciting Selihot. The Thirteen Midot should be said with a Minyan.
The Power of Prayer