Merit of Fasting
In the name of Allāh, the Most Gracious, the Most Merciful;
All the praise and Thanks are due to Allāh, the Lord of the al-ā’lamīn. I testify that there is none worthy of worship except Allāh, and that Muhammad, sallallāhu alayhi wa sallam, is His Messenger.
Islam is built on five pillars. Each represents a unique utility, an institution, if you will, through which the believer builds his relationship with the Creator and the creation.
Of all the pillars of Islam, none is more special than siyaam, fasting. While there may be an appearance of Riya, eye service, or show, in all other pillars - Solat, Zakaat, Hajj, and even the Kalimah - there is no such possibility in fasting. The only One who knows that you are really abstaining is Allah, the Almighty. It is easy to pretend to be fasting; while in hiding, you may eat or drink. Thus, fasting is considered a special worship, as Hadith reports from the Messenger of Allah (sallallāhu 'alayhi wa sallam) have detailed.
It has been reported by the way of Abu Hurairah (radiallāhu`anhu) that the Prophet (sallallāhu 'alayhi wa sallam) reported that Allah (Subhanahu Wa Ta'ala) said in a Hadith Al-Qudsi:
"All services of the son of Adam are for him except fasting. It is for me, and I will reward him for it. Fasting is a shield. On the day you fast, do not use obscenity, nor yell at others, nor act ignorantly towards them. However, if anyone abuses you verbally or attempts to draw you to fight with him, say 'I am fasting' two times. The Prophet (sallallāhu 'alayhi wa sallam) then states: I swore by the One (Allah) in whose Hand is the soul of Muhammad, the breath of the faster is sweeter to Allah on the Day of Judgment than the scent of musk. The faster experiences enjoyment twice: he is pleased when he breaks his fast, and he is pleased when he meets his Maker" (Muslim)
Among the points this incisive hadith revealed is that fasting is Allah's. Certainly, there is only one reason why a believer will put himself or she through this trying physical exercise that - to seek the pleasure of Allah (SWT). The fast is the single most important device to test the Iman, faith, of the believer and the depth of his sincerity and commitment to the concept of Tawhid, the Oneness of Allah.
The hadith also states that fasting is a shield, an armor protecting the believer from sinful acts (ma'asi). Do you not know that nourishment is the first culprit in the propagation of sins? For when you eat, the blood flow increases considerably, and the energy level increases, making it easier for Satan to use your own energy level to tempt you to commit sins. In another hadith, the Prophet states: "Satan runs in the circulatory system of the son of Adam in the same way blood circulates in our system; so tighten his passages with hunger." (Bukhari ; Muslim)
Now one could see why fasting becomes a shield. Fasting enables the believer to guard against his archenemy. It also helps him against human evil by putting the patience and perseverance gained from fasting into use with forbearance and forgiveness of the attacker - that is, of course, when the safety of ones life is not involved. Otherwise, in this case, Al-Qur'an allows the believer to repel evil without transgression.