Q. Why are the piyutim of the Selichos so complicated, and difficult to understand as they use words that are totally unknown to most of us? They probably were also challenging and cryptic to the masses in the days they were composed. So why not recite piyutim that we all can easily understand and have proper kavana?
A. In Ahavas Tzion (Drosho 12) R. S. Lando zt’l (son of the Noda Beyehuda), when stating the importance of using Lashon Hakodesh in all our tefilos and piyutim, explains that an essential part of prayer is elevating ourselves, by the expressions and idioms that we use to call on Hashem and to address Him.
Vavei Hoamudim (by the son of the Sheloh, printed in his sefer) quotes Sefer Chasidim, who exhorts and demands from the masses to establish classes and shiurim, to learn all about and to explain the meaning of “tefilos, piyutim and selichos.”
In that sense, the use of an elevated and prominent vocabulary was indeed intentional, to create the need of learning the pirush hamilos and the profound meaning of the selichos. This became an elemental and intrinsic hachana or spiritual preparation, for davening to Hashem.
Nitei Gavriel (Rosh Hashana 10: 4) writes that it is proper for one who does not understand the words said in selichos, to use a sefer that has translation and explanations.
He quotes (ibid. n. 6) that the Lebush Mordechai would indeed sit and learn the pirush hamilos of selichos, adding that tefilos he understands a bit, but selichos not so much.
Horav Shlomo Miller Shlit’a added that on the other hand, often when simple people recite tefilos they don’t understand, on the contrary, they put all their heart into them. An example would be the recitation of Kol Nidrei.
Rabbi A. Bartfeld as revised by Horav Shlomo Miller Shlit’a