And remember Our servants Ibrahim, Ishaq and Ya'qub, men of true strength and inner sight. We purified their sincerity through sincere remembrance of the Abode . (Surah Sad: 45-46)
Allah also stressed that Musa (as) reached a high level of purification. A verse states as follows:
Mention Musa in the Book. He was truly sincere and was a messenger and a prophet. (Surah Maryam: 51)
We must ponder deeply the high morality of Allah's prophets, and strive like them to become purified servants.
The Qur'an announced that only those who are blind and deaf will not benefit from the reminders and verses of Allah. True believers, on the other hand, are "those who, when they are reminded of the Signs of their Lord, do not turn their backs, deaf and blind to them." (Surat al-Furqan: 73) Those who fear Allah and guard against evil are capable of perceiving the wisdom of the verses of the Qur'an. They draw lessons from them, and thus, acquire sincerity. Therefore, believers could never be indifferent to such reminders from Allah. Even if someone has until then failed to think about the importance of sincerity, just one moment spent to check his intentions would be sufficient to purify himself. With Allah's permission, this improvement converts later deeds into pious ones, and grants the person the honor of being "the best of creatures" in Allah's sight.
Otherwise, if one sullies his deeds done to acquire Allah's assent, by letting worldly ambitions interfere and invalidates them, instead of aiming to acquire sincerity, then he will certainly be acting immorally. This person may strive day and night and consider himself guided on the straight path of morality. However, he will not be among those who turn to Allah purely, as he does not strive to acquire sincerity. Surat al-Kahf puts forth the example of such losers as follows:
Say: "Shall I inform you of the greatest losers in their actions? People whose efforts in the life of this world are misguided while they suppose that they are doing good." (Surat al-Kahf: 103-104)
However, when he looks back upon his life, he will realize that there is nothing left to indicate that he had spent those years in this world. Neither the people whose consent he strove to acquire, nor the worldly goals he pursued, nor his arrogance, nor the devil who deceived him to damage his sincerity, will stand by him. He will stand in Allah's presence alone and unaided, as he failed to turn to Him with a pure heart, and had harmed his sincerity by combining his faith, service and worship with other impurities. In Surat al-Hadid, Allah announces that this worldly life is nothing but a great deception:
Know that the life of the world is merely a game and a diversion and ostentation and a cause of boasting among yourselves and trying to outdo one another in wealth and children: like the plant-growth after rain which delights the cultivators, but then it withers and you see it turning yellow, and then it becomes broken stubble. In the hereafter there is terrible punishment but also forgiveness from Allah and His good pleasure. The life of the world is nothing but the enjoyment of delusion. (Surat al-Hadid: 20)
Would one like to see that he has been striving in vain, in spite of his greater effort, merely because he had failed to endeavor to acquire sincerity, and did not live in accordance with the spirit of the Qur'an? Or, would one like to be one of the "best of creatures" who is granted "a wage which never fails" by purifying his intentions, heart and conscience and turns to Allah with heartfelt devotion, firmly embraces Him, and desires to acquire nothing but His consent? It is apparent that, for anyone who loves Allah, and who wishes to befriend Him and to turn to Him, the latter option is the only option to be taken.
Therefore, with this book, we are inviting all those sincere believers, who love Allah, wish to befriend Him, and turn to Him, to search for the secret that leads to being among the successful. As Bediuzzaman mentioned, a single deed performed sincerely may well be more precious than thousands of insincere ones. Always keep in mind that if your intentions are sincere, and your deeds are pious; even the most trivial of them which you perform for Allah's sake, will not go unnoticed by Him. Because as He informed us in the Qur'an, "Your Lord knows best what is in your selves. ..." (Surat al-Isra': 25) and "…Allah knows those who have do their duty." (Surah Al 'Imran: 115)