To what extent is it true that the verse (And We shall turn to whatever deeds they did and make them as scattered dust) is the most frightening verse in the Qur’an and speaks about the fate of the deeds of Muslims who have lost sincerity in them?

Worship of Allah is based on sincerity and adherence, which are the foundation of all acts of worship and the aim of the Prophets. Whoever intends the Face of Allah in his righteous deed will succeed, and whoever seeks worldly gain will lose his deed. Ostentation (riya') nullifies the reward of a deed, for the Prophet (PBUH) said: "I am the One Who is Most Self-Sufficient, Most Needy of no partner. Whoever performs a deed and associates someone else with Me therein, I shall abandon him and his shirk (definition)."

The Hadith (definition) of Thawban indicates that some people will come with great good deeds on the Day of Resurrection, but these deeds will be made like scattered dust. These are the ones who violate the sacred limits of Allah in private.

As for the deeds in which a servant was sincere to Allah, they are not nullified by the occurrence of ostentation in other deeds or by committing sins, for Allah the Almighty says: "So whoever does an atom's weight of good will see it, And whoever does an atom's weight of evil will see it." Allah rewards for accepted deeds, even if the one who performed them is disobedient in other matters.

The Holy Quran is full of verses of intimidation that motivate believers to fear Allah, such as His saying: "And fear the Fire which has been prepared for the disbelievers," and "Indeed, mankind is in loss, Except for those who have believed and done righteous deeds and advised each other to truth and advised each other to patience."