How can the sweetness of faith and devotion in prayer be restored after losing them, along with forgetting the Qur'an and declining academically?

Faith increases with acts of obedience and decreases with acts of disobedience. Its sweetness is attained through knowledge of Allah, His Names, and His Attributes, and through knowledge of the Prophet, peace be upon him, his life, and his worship, as well as through obedience to Allah, avoidance of His wrath, contentment with Allah as Lord, with Islam as a religion, and with Muhammad as a Messenger, and through loving and hating for the sake of Allah. The Messenger of Allah, peace be upon him, said: "There are three qualities, whoever has them will taste the sweetness of faith: that Allah and His Messenger are dearer to him than anything else; that he loves a person only for the sake of Allah; and that he hates to return to disbelief as he hates to be thrown into the Fire." And he said: "He has tasted the sweetness of faith who is content with Allah as Lord, with Islam as a religion, and with Muhammad as a Messenger." Similarly, reciting the Quran polishes the hearts, and forgetting it is one of the greatest sins. The Prophet, peace be upon him, said: "Guard this Quran, for by Him in Whose Hand is the soul of Muhammad, it is more liable to escape than camels in their ropes." Maintaining this and performing prayers in congregation restores religiosity, the sweetness of faith, and devotion.