Likutei Moharan 155:1/ליקוטי מוהר"ן קנ״ה:א׳

1Sadness is a very evil trait. And, a person’s not traveling to the tzaddik is due to sadness and sluggishness <and slothfulness>.

2Likewise, a person’s not praying <or studying Torah with inspiration and intensity> is due to sadness and slothfulness—i.e., due to a lack of faith. For certainly, if he had perfect faith and believed that God is close to him and hears every single word that comes from his mouth, and hearkens to the sound of his prayer, he would definitely not have any sadness, slothfulness or sluggishness in his prayers. And he would certainly pray properly.

3However, the confusion of prayer is mainly due to a lack of faith. As a result, slothfulness and sadness beset him and muddle his prayer. For sadness and the slothfulness are primarily due to a lack of faith.

4This is similar, for example, to placing wheat in good earth. It then grows and sprouts well, and is not harmed by any winds, storms or thunder. This is because <it> has the power to sprout and the power to grow, and so nothing harms it. But when the wheat is put in earth unsuitable for sowing, it then rots in the earth because it has neither the power to sprout nor the power to grow.

5Now, EMuNah (faith) is an aspect of growing power and sprouting power. As it is written (Esther 2:7), “And ŒMeiN (he raised) Hadassah”—an expression connoting growth. As our Sages teach: Faith—this is the Order of Zera’im (Seeds) (Shabbat 31a). Therefore, when one has faith, which is the aspect of growing power and sprouting power, he is then not harmed by any <obstacle>, and he is not afraid of anybody or anything. He prays with proper vitality and travels to the tzaddik, for he is neither frightened by nor afraid of anything in the world.

6But when <he> lacks faith, he then does not have the power to grow and the power to sprout. In that case, he literally rots, like the aforementioned wheat. As a result, he experiences sadness, slothfulness and sluggishness, and literally rots.