Here Allah mentions the destiny of the righteous in the Hereafter, those who believe in Allah and His Messenger and do righteous deeds in accordance with the Laws of Allah.
(for them are Gardens of Delight.) means, there they will enjoy all kinds of delights and pleasures, food, drink, clothing, dwelling-places, means of transportation, women, a light of beauty and delightful sounds, which have never crossed the mind of any human being. They will stay there forever, never leaving and never desiring change.
(It is a promise of Allah in truth.) meaning, this will undoubtedly come to pass, for it is a promise from Allah, and Allah never breaks His promise, because He is the Most Generous Bestower Who does what He wills and is able to do all things.
(And He is the All-Mighty,) Who has subjugated all things and to Whom all things submit,
(the All-Wise.) in what He says and what He does, Who has made this Qur'an a guidance to the believers.
(Say: "It is for those who believe, a guide and a healing. And as for those who disbelieve, there is heaviness (deafness) in their ears, and it is blindness for them) (41:44).
(And We send down of the Qur'an that which is a healing and a mercy to those who believe, and it increases the wrongdoers nothing but loss.) (17:82)