​MN 16 16 Cetokhila Sutta: The Wilderness in the Heart 

Thus have i heard.

On one occasion the Blessed One was living at Savatthi in Jeta's Grove, at Anathapindika's Park. There he addressed the bhikkhus thus: "Bhikkhus,  any bhikkhu who has not abandoned five wildernesses in the heart and not severed five shackles in the heart; it is impossible for them to grow, increase and achieve fulfillment in this Dhamma and Discipline." 

"What bhikkhus, are the five wildernesses (mental desolation) in the heart that he has not abandoned?

1. Here a bhikkhu is doubtful, uncertain, undecided and un-confident about the Teacher and thus his mind does not incline to ardor, devotion, perseverance, and striving. As his mind does not incline to ardour, devotion, perseverance, and striving, that is the first wilderness in the heart that he has not abandoned.
2. Again, a bhikkhu is doubtful, uncertain, undecided, and un-confident about the Dhamma ...as his mind does not incline to ardor...that is the second wilderness in the heart that he has not abandoned.
3. Again a bhikkhu is doubtful, uncertain, undecided, and un-confident about the Sangha...As his mind does not incline to ardor...that is the third wilderness in the heart that he has not abandoned.
4. Again, a bhikkhu is doubtful, uncertain, undecided, and un-confident about the training...As his mind does not incline to ardor.. .that is the fourth wilderness in the heart that he has not abandoned.
5. Again, a bhikkhu is angry and displeased with his companions in the holy life, resentful and callous towards them, and thus his mind does not incline to ardor, devotion, perseverance, and striving. As his mind does not incline to ardour, devotion, perseverance, and striving, that is the fifth wilderness in the heart that he has not abandoned. These are the five wildernesses in the heart that he has not abandoned." 

"What, bhikkhus, are the five shackles (mental imprisonments) in the heart that he has not severed?

1. Here a bhikkhu is not free from lust, desire, affection, thirst, fever, and craving for sensual pleasures, and thus his mind does not incline to ardor, devotion, perseverance, and striving. As his mind does not incline to ardor, devotion, perseverance, and striving, that is the first shackle in the heart that he has not severed.
2. Again, a bhikkhu is not free from lust, desire, affection, thirst, fever, and craving for the body....As his mind does not incline to ardor.. .that is the second shackle in the heart that he has not severed.
3. Again, a bhikkhu is not free from lust, desire, affection, thirst, fever, and craving for form...As his mind does not incline to ardor...that is the third shackle in the heart that he has not severed.
4. Again, a bhikkhu eats as much as he likes until his belly is full and indulges in the pleasures of sleeping, lolling, and drowsing...As his mind does not incline to ardor...that is the fourth shackle in the heart that he has not severed. 5. Again, a bhikkhu lives the holy life aspiring to some order of gods thus: 'By this virtue or observance or asceticism or holy life, I shall become a great god or some lesser god and thus his mind does not incline to ardor, devotion, perseverance, and striving. As his mind does not incline to ardor, devotion, perseverance, and striving, this is the fifth shackle in the heart that he has not severed.
These are the five shackles in the heart that he has not severed."

"Bhikkhus, anyone who has not abandoned these five wildernesses in the heart and severed these five shackles in the heart  will not come to growth, development, and fulfillment in this Dhamma and Discipline. On the other hand, any bhikkhu who has abandoned five wildernesses in the heart and severed five shackles in the heart will come to growth, development, and fulfillment in this Dhamma and Discipline. "
 "What, bhikkhus, are the five wildernesses in the heart that he has abandoned?"

Here a bhikkhu is not doubtful, uncertain, undecided, or un-confident about the Teacher, Dhamma, Sangha, the training and companions in the holy life and thus his mind inclines to ardor, devotion, perseverance, and striving. As his mind inclines to ardor, devotion, perseverance, and striving, the five wilderness in the heart have been abandoned by him. 

"What, bhikkhus, are the five shackles in the heart that he has severed?"

Here a bhikkhu is free from lust, desire, affection, thirst, fever, and craving for sensual pleasures,body, form, over eating, sleeping, drowsiness, does not live the holy life and aspiring to some gods and thus his mind inclines to ardor, devotion, perseverance, and striving. As his mind inclines to ardor, devotion, perseverance, and striving, the five shackles in the heart have been severed by him. 

"Bhikkhus, if anyone who has abandoned these five wildernesses in the heart and severed these five shackles in the heart  then they will come to growth, development, and fulfillment in this Dhamma and Discipline.
He develops the basis for spiritual power consisting in concentration due to
- zeal and determined striving
- energy and determined striving
- purity of mind and determined striving
- investigation and determined striving
- enthusiasm

"A bhikkhu who thus possesses the fifteen factors including enthusiasm is capable of breaking out, capable of enlightenment, capable of attaining the supreme security from bondage. Suppose there were a hen with eight, ten, or twelve eggs, which she had covered, incubated and nurtured properly. Even though she did not wish: ' 'May the chicks pierce the eggshells with their claws or beaks and break through safely,' yet the chicks are capable of piercing their shells with the points of their claws and beaks and hatching out safely on their own. So too, a bhikkhu who thus possesses the fifteen factors including enthusiasm is capable of breaking out, capable of enlightenment, capable of attaining the supreme security from bondage." 

That is what the Blessed One said. The bhikkhus were satisfied and delighted in the Blessed One's words. 
In summary, Buddha talked about the five wilderness (mental desolation) of the heart namely doubts about the Teacher, about the Dhamma, about the Monks Order and the course of training and companions in holy life and the five shackles (mental imprisonments) namely attachment to sensual pleasures, to the body, to visible forms, over-eating, desire to be born among the gods. If a monk cannot abandon the five wilderness of the heart and the five shackles, they cannot possibly show growth, develop and progress in the Dhamma and the Vinaya. ​
References: 
1. www.accesstoinsight.org
2. https://suttacentral.net/
3. The long discourses of the Buddha (Bhikkhu Bodhi)