Sefer Tiferes Shmuel (Ois 4) writes that although humility and lowliness are good middos, the yeitzer hara can use them to make a person depressed. It can convince him that his Torah and tefillah are worthless since he is unworthy, and this can cause a person to lose and become sad.
To counter this, Chazal say (Sanhedrin 37A) that one should say that the world was created just for him. This means that one should recognize that his soul is pure and holy and his faults are merely external. When one accepts this fact, he will know that Hashem does desire his Torah and tefillah, and he will not be fooled by the yeitzer hara.
In this vein, Rashi states (Shemos 27:20): “Crushed for lighting and not crushed for Menachos.” Tzadikim explain this to mean that one should be “crushed” – he should be humble and lowly – but only “for lighting”, meaning that this should be used as a means of lighting up oneself to serve Hashem properly. One should not be crushed “for Menachos”, meaning that his humility should not make him rest (munach) from serving Hashem. One should not have “anavah pesulah”, improper humility that impedes his avodas Hashem.
This is also seen from the Mishnah (Avos 2:13) that states: “Be careful with Kriyas Shema and tefillah... and don’t be a rasha in your own eyes.” This can be understood to mean that one should not despair and think he can’t daven and say Kriyas Shema because the yeitzer hara tells him that he is unworthy. Rather, one should make sure to daven and serve Hashem and trust that He desires his tefillos, even though he is lowly. This is as Dovid Hamelech says (Tehillim 22:25): “For He does not shame and He does not abhor the humility of a poor man.... And when he calls to Him, He hears.” Even if one is “poor” in his avodas Hashem, He hears his prayers.
This is hinted to in the pasuk’s word “l’nefesh”. This refers to things pertaining to the soul, i.e., avodas Hashem. It says “lo yitamu b’amav”, meaning that one should not allow the yeitzer hara to convince him that he is too impure and lowly to serve Hashem. Rather, one should continue to serve Him and trust that He will accept his avodah, even though he is lowly.
