• The letter Nun stands for the word nefilah which means falling. This word has a negative connotation since it is used regarding the fall of the Jewish people as it is written “She ( the Jewish people) has fallen (nuf’lah) no longer will the maiden of Israel stand again.” (Amos 5.2) Therefore King David did not include this letter when writing Ashrei.
* Mizmor letodah ( psalm 100) is part of the daily prayer service recited as part of the songs of thanksgiving in Pesukei Dezimra. It represents the Thanksgiving offering which thanks G-d for having been saved from dangers we face everyday even though we may be unaware of these dangers.
• Psalm 100 is left out on Shabbat and Yom tov ( festivals, chol ha med of Pesach and the days before