In The Name of Allaah, The Most Merciful, The Bestower of Mercy.
Imaam Ibnul Qayyim [may Allaah have mercy upon him] stated: Righteousness of the heart and its steadfastness upon the path leading to Allaah’s (good Pleasure) depends on its complete devotion to Allaah [The Most High]. The heart cannot be rectified except through turning completely to Allaah (in obedience, submission); but excess food and drink, excess intermingling with the people, excess speech and sleep are some of (those things) that increase the heart in decay, distracts it in every way and isolates it from its path of (obedience) to Allaah [The Most High] – either weakening or hindering it, or preventing it (from this goal). Therefore, Allaah’s Mercy necessitates that fasting is legislated for the (believing) servants in order to (divert them) from excess food and drink, and rid the heart of the intrusions of desires, which hinders it from its path (of obedience) to Allaah. Allaah legislated (fasting) in accordance with what is of benefit for the servant, so that the servant is benefited in his worldly life and afterlife – neither hindering him from what will bring about well-being for him in this life nor in the afterlife. (1)
Imaam Ibnul Qayyim [may Allaah have mercy upon him] also said: The fasting person is the one whose limbs abstain from sins- tongue (abstains) from lying, lewdness and false speech, stomach (abstains) from food and drink, and his private parts (abstain) from obscenity. When he speaks, he does not speak with what harms his fasting and when he acts he does not do what corrupts his fasting. All his speech comes out useful and righteous. Likewise his actions are of the status of the scent that is smelled by the one who sits with the seller of musk; therefore, the one who sits with the fasting person is benefited and saved from false speech, lies, evil deeds and oppression. This is the legislated fasting and not merely abstaining from food and drink. And it is (reported) in the authentic hadeeth, “Whoever does not give up lying speech (false statements) and acting on those lies and evil actions, Allaah is not in need of his leaving his food and drink”. (2)
[Ref 1: Source: Zaadul Ma’aad’ with annotations by Imaam Abdul Bin Abdul Azeez Bin Baaz & Checking of the Ahaadeeth by Imaam Albaani (may Allaah have mercy on both of them). Vol 2. Page 39. Publisher: Daarul Aathaar’ 1st ed. ISBN Number: 2005/9441]
[Ref 2: Sharh Al-Waabilus Sayyib by Imaam Abdul-Azeez Bin Baaz (may Allaah have mercy upon him). page:31]