The fact that he is abstaining from food and drink both in public and in secret shows his honest faith and strong love of Allah, and his knowledge and feeling that Allah is all-knowing of everything. For this reason Allah has made the reward for fasting greater than for any other type of worship:
Allah said in the hadith Qudsi:
"Every deed of the son of Adam will be multiplied [in rewards], the good deed by ten of its like, up to seven hundreds, up to whatever Allah wills, except fasting, it is for Me and I will reward it . He abandons his desire and his food for my sake.." (Related by Muslim)
Ibn al-Qayyim said:
"...And people may see that a person is not eating in front of them, but the fact that he is really abandoning his food and his desire for the sake of God is a thing that nobody can find out about, and that is the essence of fasting." (Zaad al-Mi'ad 2/29).
Relieving Muslims from life's distractions:
Eating, drinking, and socializing all distract a person and weaken ties with Allah. It is by the Mercy of Allah that Muslims are ordered to fast so as not be bothered by the intrusion of these activities. Nor by the thought about them nor the anticipation for them when devoting themselves to the all types of worship Either reading the Qur'an, offering additional prayer or making I'tikaf.
For this reason the Prophet (SAW) said:
"Fasting is a shield, and a secure fortress against Hell fire" (Related by Ahmad).