In his commentary to Berachos 32b, the Meiri offers another reason for the placement of Aleinu at the culmination of the prayer service. Just as it is appropriate and commendable to pause prior to davening to think about before Whom we stand and what we are going to say, it is, likewise, proper to take a step back at the end of our prayers to reflect on what we have said and to Whom we have spoken. A “hit and run” davening is neither respectful nor particularly effective. It defeats the entire purpose. It is almost as if we had unloaded a heavy load, dropped it off, and ran away.
The Chida, zl, offers an alternative explanation which he saw in a manuscript authored by Rav Vidal HaTzarfati. One should not think that, once he has completed davening, he has fulfilled his obligation to Hashem and he can now go along his merry way. The Aleinu tefillah indicates that, even after one has successfully completed the davening and has done so with complete kavanah, concentration and devotion, he must still praise Hashem for selecting us as His People.
