The sawm is one of the Furu' al-Din (the duties to be performed according to Islamic Shari'ah) of the holy religion of Islam. It is wajib upon every mukallaf to have sawm in the month of Ramadan. In order to obey the command of Allah, from the time of Salatal-Fajr to the time of Salat al-Maghrib one must refrain from muftirat (certain acts which break or invalidate the sawm) which make the sawm batil.
In Islam, much importance has been attached to sawm. Islam maintains a great deal of value for this holy act. The reward and recompense of sawm is so vital in Islam that the Almighty Allah without His prior specifying the thawab and the recompense of sawm, ascribes its reward to Himself.
The Holy Prophet (S) said that Allah stated: "The sawm is for Me and I will give reward for it."
With its specific characteristics, the sawm plays an exceptionally effective role in the liberation of man from the servitude of ambitions, carnal desires, voluptuousness as well as in the purification of the soul from involvement in sinful acts.
The Holy Prophet (S) told Jabir ibn 'Abdillah al-Ansari: "O Jabir, this is the month of Ramadan and the one who has sawm during the day and stays awake at night to commune with Allah, abstains from eating haram food, and guards against evils and using abusive language, gets out of sins as he leaves the month of Ramadan behind."
Jabir said: "O Prophet (S) of Allah, what a good news is it!" The Holy Prophet (S) stated: "O Jabir, how demanding and exacting are the conditions for the sawm!"
Al-'Imam al-Sadiq (as) has stated: "The sawm serves as a strong shield against the fire of the Hell."

Ramadan, The Month of Allah
In Islamic ahadith many praiseworthy and interesting names such as "the auspicious month" and "the best period for the recital of Qur'an" have been mentioned for the month of Ramadan. But the name "the month of Allah" is the most outstanding name and the most beautiful title which has been used for the month of Ramadan.
In spite of the fact that every month is "Allah's month", this month is specifically called "the month of Allah" due to its great importance. Thus this name has in itself endowed this month with a special superiority and a specific spirituality. In this month, the greatest Divine Book (the Holy Qur'an) has been revealed.
With the advent of the holy month of Ramadan, Allah bestows His servants with His blessings. A special enlightenment and serenity generate in the spirit of man. For the worshipping of Allah, the purification of the soul, and moral reformation, a special preparedness becomes manifest in those who have sawm.
On the last Friday of the month of Sha'ban, the Holy Prophet (S) stated the following concerning the magnificence and value of "the month of Allah".
"O people, the month of Allah, along with its blessings and salvation, has revealed itself to you. It is a month which is regarded as the best of all the months by Allah. Its days, nights, and hours are the best of all. It is a month in which you are invited to be the guest of Allah and are entitled to His favour and generosity."
"In this month, your breathing will have the thawab of tasbih saying"Subhanallah" (Glory be to Allah) and dhikr and your sleeping will have the thawab of the worship of Allah."
"If you resort to Allah in this month and worship Him, Allah will grant your prayers. Therefore, with all your truthfulness and sincerity and with a pure heart pray to Allah to grant you His Divine dispensations for having sawmand reciting the Holy Qur'an, for one who remains deprived of the forgiveness and blessings of Allah in this bountiful and blessed month is indeed unfortunate."

The Sawm Leads To Taqwa
The Almighty Allah states in the Holy Qur'an: "O you who believe! the sawm is prescribed for you, as it was prescribed for those before you, so that you may have taqwa (2:183)."
Islam enjoins its followers to have sawm for a complete month (during the month of Ramadan). By having sawm for one month, Muslims prepare themselves for the state of taqwa in its entirety, because when a man refrains from satisfying his natural physical desires, he can very well abstain from satisfying his carnal desires.
In order to attain such a degree of perfection, Islam surely does not consider only abstaining from eating and drinking to be sufficient for the sawm, rather it orders a person who has sawm to abstain from whatever causes indulgence in evils and the commitment of sins or leads him to satanic temptations and indulgence in his unruly carnal desires.

Muftirat Which Render the Sawm Batil
Several muftirat (certain acts which invalidate the sawm) render the sawm batil. These include the following:
(i) Eating and drinking, although these things may not be usual drinks or eatables such as soil or the gum of trees.
(ii) The sexual intercourse renders the sawm batil.
(iii) Masturbation, that is, engagement in any sexual activity which leads to seminal ejaculation.
(iv) Ascribing a lie to Allah, the Holy Prophet (S), and the successors of the Holy Prophet (S).
(v) Allowing thick dust to reach one's throat.
(vi) Immersing the head entirely in water.
(vii) Remaining in the state of janabah, hayd and nifas up to the Adhan forSalat al-Subh.
(viii) Application of an enema with a liquid substance.
(ix) Vomiting, provided that it is done deliberately.
For further information, reference should be made to al-risalat al-'amaliyyah (Islamic treatises written by mujtahidin for use by theirmuqallidin for performing Islamic duties).