The purpose behind fasting is to restrain the soul from desires and to wean it from those things which it has become accustomed to; and to balance the soul’s force of desire, so that it can be prepared to attain wherein lies the utmost degree of happiness and delight for the soul, and the acceptance of what purifies it for its eternal life. (By fasting) one curbs his hunger and thirst from its sharpness and intensity, and is reminded of the conditions of the hungry stomachs of needy people. (By fasting) one narrows the passageways of Shayṭān within the servant (of Allāh), by narrowing the passageways of food and drink. As well, it restrains the force of the limbs from giving way to its dominating nature of that which is harmful to it in this world and the hereafter. And, (fasting) subdues every limb and might of the soul from (following its) whims, and harnesses it by its bridle. For, surely (the fast) is the bridle of the muttaqūn [the righteous, those having taqwá] and the shield of the warriors [a shield between them and the Hell-fire]. And, it is the (spiritual) exercise of the Abrar [the pious and righteous] and those nearest [to Allāh]. And, it is (done) for the Lord of the Worlds, out of all actions [implemented for Allāh’s sake]. For the fasting person does nothing; he merely abandons his desires, his food and drink for the sake of the One whom he worships. Therefore, (fasting) is abandoning those things beloved and desired by the soul, favouring instead Allāh’s love and contentment. And, it is a secret between the servant and his Lord, no one else aware of it, but Him. And the servants (of Allāh) might be aware of (his) outward abandoning from the things which breaks the fast. However, as for him abandoning his food, drink and desires for the sake of the One whom he worships, then that is something mankind is unaware of and, surely that is the reality of fasting.

لما كان المقصود من الصيام حبس النفس عن الشهوات وفطامها عن المألوفات وتعديل قوتها الشهوانية لتستعد لطلب ما فيه غاية سعادتها ونعيمها وقبول ما تزكو به مما فيه حياتها الأبدية ويكسر الجوع والظمأ من حدتها وسورتها ويذكرها بحال الأكباد الجائعة من المساكين .

وتضيق مجاري الشيطان من العبد بتضييق مجاري الطعام والشراب وتحبس قوى الأعضاء عن استرسالها لحكم الطبيعة فيما يضرها في معاشها ومعادها ويسكن كل عضو منها وكل قوة عن جماحه وتلجم بلجامه فهو لجام المتقين وجنة المحاربين ورياضة الأبرار والمقربين وهو لرب العالمين من بين سائر الأعمال فإن الصائم لا يفعل شيئا وإنما يترك شهوته وطعامه وشرابه من أجل معبوده فهو ترك محبوبات النفس وتلذذاتها إيثارا لمحبة الله ومرضاته وهو سر بين العبد وربه لا يطلع عليه سواه والعباد قد يطلعون منه على ترك المفطرات الظاهرة وأما كونه ترك طعامه وشرابه وشهوته من أجل معبوده فهو أمر لا يطلع عليه بشر وذلك حقيقة الصوم

Source: Zaadul Ma’ad, 2/28-29
Translated by Umm Sufyān