Musar su Salmi 119:10

By the same token, a person who prays at length and is not answered should not despair of praying again. For the Holy One Blessed is He does indeed desire his prayers but He desires that they be with proper intent. That is, the heart must concentrate and know what the mouth utters. Thus the Zohar warns in Parashas Beshalach (63b): We have been taught: Whoever prays before the Holy King must make his request and pray his prayer from the depths of his heart so that he is wholeheartedly with the Holy One Blessed is He. Moreover, he must concentrate his mind and will on what he is uttering. Thus said King Dovid, “I have sought You with my entire heart, etc.” (Tehillim 119:10).