Hadrat Imam-i Rabbani states the following about this subject:
The blessed month of Ramadan is very honorable. The rewards given for the voluntary prayer, remembrance of Allah, alms, and all other such worships done in this month are like those given for the obligatory ones done in other months. One obligatory act of worship done in this month is like seventy obligatory acts of worshipdone in other months. If a person gives (the supper called) iftar to a fasting person in this month, his or her sins will be forgiven. He or she will be emancipated from Hell. In addition, he or she will be given as many rewards as those which the fasting person receives. The rewards of that fasting person will not decrease in the slightest degree.

In this month, also those bosses who facilitate the work of those under their commands and who make it easy for them to worship will be forgiven. They will be emancipated from Hell. In the blessed month of Ramadan, the Messenger of Allah used to emancipate the slaves and would give whatever was asked from him. Those who can do good deeds in this month will be blessed with doing such deeds all the year round. If a person disrespects this month and commits sins in this month, he or she will spend all the year sinning.

We should consider this month as an opportunity. We should perform as many acts of worship as we can, do the deeds which Allahu ta’ala likes, and deem this month an opportunity for earning the next world.

The Qur’an al-karim descended in the month of Ramadan. The Night of Qadr is in this month. In holy Ramadan, it is an act of sunnat to have the iftar early and to have the sahur (pre-dawn meal) late. The Messenger of Allah was careful about performing these two sunnats.

Maybe hurrying for the iftar and being late for the sahur show humans’ incapacity and that they need to eat and drink, and consequently, everything. And this is the meaning of worshiping.

It is a sunnat to have the iftar with a date. It is an important sunnat to recite the prayer, Zahabazzama’ wabtallat-il uruq wa thabat-al-ajr insha-Allahu ta’ala” after breaking the fast, to perform the namaz of Tarawih, and to read a khatm (that is, to read the entire Qur’an al-karim).
In this month, thousands of those Muslims who are to go to Hell are forgiven and emancipated every night. In this month, the gates of Paradise are opened. The gates of Hell are closed. The devils are chained. The doors of compassion are opened. May Allahu ta’ala bless us all with the lot of worshipping Him in a manner worthy of His greatness and with being on the right way which He likes! Amen. (Maktubat, Vol. 1, Letter 45)

Those who do not fast and who eat in public are not respectful to this month. Even people who do not perform namaz must fast and avoid the prohibited actions. Such people’s fasting is accepted and is a symptom of their faith.

It is very thawab to fast in the blessed month of Ramadan, and it is a grave sin not to fast without a good excuse. A hadith-i sharif says, “If a person does not fast for a single day in Ramadan without a good excuse, he cannot earn the thawab of this single day, even if he fasts all the year round instead of it” [Tirmidhi].

(If there is a religiously legitimate excuse, then it is not sinful not to fast.)

Some hadith-i sharifs about fasting in Ramadan are as follows:
(The month of Ramadan is a blessed month. Allahu ta’ala made fasting in Ramadan obligatory for you. In this month, the gates of compassion are opened, and the gates of Hell are closed. The devils are put in chains. In this month is a night which is more valuable than a thousand months. Whoever is deprived of the goodness of that night [the Night of Qadr] has been deprived of all goodness.) [Nasai]

(If a person fasts by knowing it as fard to fast in the month of Ramadan and by expecting its thawab from Allahu ta’ala, his sins are pardoned.) [Bukhari]

(If a person dies after fasting in Ramadan, he will go to Paradise.) 

(When the month of Ramadan comes, it is said, “O seekers of goodness, run to what is good. O seekers of evil, abstain from what is evil.”) [Nasai]

(Ramadan is the month of barakah. In this month, Allahu ta’ala forgives sins and accepts supplications. Fulfill the rights of this month. Only he who will go to Hell does not become the beneficiary of compassion in this month.) 

(When the holy month of Ramadan comes, Allahu ta’ala orders angels to pray for forgiveness of Believers.) [Daylami]

(An obligatory namaz becomes atonement for the sins committed up to the next namaz. A Friday becomes atonement for the sins committed up to the next Friday. The month of Ramadan becomes atonement for the sins committed up to the next Ramadan.) [Tabarani]

(He who can fast for three consecutive days must observe the fast of Ramadan.) [Abu Nu’aym]

(The fast of Ramadan is fard and Tarawih is sunnat. If a person fasts in this month and spends its nights performing acts of worship, his sins are forgiven.) [Nasai]
(The reason why this month is called Ramadan is that it burns and melts sins.) [I. Mansur]

(The beginning of Ramadan is mercy. Its middle is forgiveness, and its end is emancipation from Hell.) [Ibn Abi ad-Dunya]

(Islam is to say Kalima-i shahadah, to perform namaz, to give zakat, to fast in the month of Ramadan, and to make a pilgrimage [to Mecca].) [Muslim]

(The beautiful mansions in Paradise will be given to those who are honey-tongued, whose salams are many, who offer meals, who observe the fast, and who perform namaz at nights.) [Ibn Nasr]

(A fasting Believer’s silence is regarded as tasbih [glorification of Allahu ta’ala], and his sleep is regarded as an act of worship. His prayer is accepted, and the reward for his good deeds is multiplied.) [Daylami]

(Do not utter obscene speech especially when you are fasting. If anyone aggresses against you, say to him, “I am fasting.”) [Bukhari]

(The true fast is the one observed not only by leaving eating and drinking but also by leaving vain speech and foul language.) [Hakim]

(Only fasting people will sit Allahu ta’ala’s table spread that is full of blessings that no eye has ever seen, no ear has ever heard, and no mind has ever imagined.) 

(Whoever observes fast for a day in the way of Allah, Allahu ta’ala keeps him seventy years’ distance away from Hell.) [Bukhari]

(Cleanliness is half of faith, and fasting is half of patience.) [Muslim]

(If a person dies while being in a state of fasting, thawab is recorded for him as if he fasted until Doomsday.) [Daylami]

(He who dies while fasting enters Paradise.) 

(A person who fasts and performs namaz will get his reward on the Day of Judgment in proportion to the degree of his aql.) [Hatib]
(Fasting curbs lust.) [Imam-i Ahmad]

On blessed occasions, we should strictly avoid sins and increase righteous deeds, acts of worships, and all kinds of charitable acts. Those who are liked by Allahu ta’ala engage in virtuous deeds at virtuous times, while those who are disliked by Him engage in evil deeds at virtuous times. This demeanor of those who engage in evil actions causes the torment they will suffer to become more severe and causes Allahu ta’ala to dislike them much more because such people, by doing so, have left themselves destitute of the blessings of these times and have violated the sanctity and honor of them. (Maw’iza-i hasana)

The dream of our master the Prophet
(I saw astonishing things in my dream. 
[In my dream] the Angels of Torment grabbed someone from my Ummah. Ablutions he had performed came and saved him from the difficult situation he was in. I saw someone being squeezed in his grave. The namâzes he had offered came and saved him from the torment of the grave. The devils were pestering someone. The remembrances [dhikr] he had made came and saved him from the devils. One’s tongue stuck out as a result of a raging thirst. The fasts he had observed in Ramadan came and quenched his thirst.

Someone was encircled by darkness. The pilgrimage he had made came and delivered him from darkness. The Angel of Death came to someone. The kindnesses he had done to his parents came. They averted death and delayed it. Someone was not allowed to talk to Muslims. Then sila-i rahm 
[visiting relatives, good treatment towards them, maintaining good ties with them] came and made intercession for him, so he could talk to them. Someone who wanted to go near his Prophet was being prevented from going. The ghusls he had taken brought him near me. Someone desired protection from the Fire. His voluntary charities came and became a veil against the Fire. When the Angels of Hell were taking someone to Hell, his enjoining the doing of what was good and forbidding the doing of what was evil came and saved him. Someone was thrown into Hellfire. The tears he had shed out of fear of Allah came and saved him.

When the deed-book of a person was being given to him from his left, his fear of Allah came and carried it to his right. Someone’s thawab weighed light. His children who had died before himself came and made it heavy. Someone was quaking with fear by Hell. When his husn-i zann [having a good opinionof] about Allahu ta’ala came, his quaking ceased. Someone who crossed the Sirat with difficulty came to Paradise, but the gates were closed. His Kalima-i shahadah came and put him into Paradise.) [Tabarani, Hakim-i Tirmidhi]

Question: Since it is the devils that cause us to commit sins, how do the devils, who are chained during Ramadan, make us commit sins?
Not only the devils but also our nafs cause us to commit sins. The harm of the nafs is much more than that of the devil. Every desire of the nafs is to its own loss. What drives us into sins in Ramadan is our nafs. The devils cannot insinuate evil suggestions (waswasa) as they are tied. In Ramadan, yawning is not from the devil. Stress-related yawns happen for such reasons as fatigue or lack of sleep. (Maktubat-i Rabbani)

What is the importance of the month of Ramadan?