Allah The Almighty has created all of creation to worship Him, and He sent Messengers to people so they would worship Him alone with no partner.

Allah The Almighty Says (what means):

• “And they were not commanded except to worship Allah, [being] sincere to Him in religion” 

(Quran 98: 5)
• “And We sent not before you any messenger except that We revealed to him that, “There is no deity except Me, so worship Me.” 

(Quran 21: 25)

• “And We certainly sent into every nation a messenger, [saying], “Worship Allah and avoid Taaghoot.” 

(Quran 16: 36)

Allah The Almighty cannot be worshipped perfectly except by dedicating all acts of worship to Him in all sincerity.

Sincerity is the basic building block of religion, the essence of worship, and prerequisite for the acceptance of any action. It is like the foundation of a building and the soul to the body. Therefore, Allah The Almighty made the actions of non-Muslims like dust dispersed because they lack the essential two elements: belief in the oneness of Allah The Almighty and sincerity. Allah The Almighty Says (what means): 

“And We will regard what they have done of deeds and make them as dust dispersed.” 

(Quran 25: 23)

Such loss will be the fate of all those who did not sincerely dedicate their worship to Allah The Almighty, and those who sought with it other than Allah The Almighty. Allah The Almighty Says (what means): 

“Whoever desires the life of this world and its adornments – We fully repay them for their deeds therein, and they therein will not be deprived. Those are the ones for whom there is not in the Hereafter but the Fire. And lost is what they did therein, and worthless is what they used to do.”

(Quran 11: 15-16)

The loser in the true sense of the word is the one who performs numerous deeds and then Allah The Almighty makes them as dust dispersed and throws him in Hellfire on his face. Abu Hurayrah, may Allah be pleased with him, narrated a Marfoo‘ Hadeeth that reads:

“The first one among the people to be judged on the Day of Resurrection will be a man who was martyred. He will be brought and Allah will remind him of His blessings and he will acknowledge them. He will say: ‘What did you do with them?’ He will say, ‘I fought for Your sake until I was martyred.’ He will say: ‘You are lying; rather you fought so that it would be said that you were brave, and that was said.’ Then He will order that he be dragged on his face and thrown into Hell. “And there will be a man who acquired knowledge and taught it, and recited the Quran. He will be brought and Allah will remind him of His blessings and he will acknowledge them. He will say: ‘What did you do with them?’ He will say, ‘I acquired knowledge and taught it, and I recited the Quran for Your sake.’ He will say: ‘You are lying; rather, you acquired knowledge so that it would be said that you were a scholar, and you recited the Quran so that it would be said that you were a reciter, and that was said.’ Then He will order that he be dragged on his face and thrown into Hell. “And there will be a man to whom Allah gave abundant wealth of all kinds. He will be brought and Allah will remind him of His blessings and he will acknowledge them. He will say: ‘What did you do with them?’ He will say, ‘I did not leave any way that You like charity to be spent but I spent charity for Your sake.’ He will say: ‘You are lying; rather, you did that so that it would be said that you were generous, and that was said.’ Then He will order that he be dragged on his face and thrown into Hell.”

[Muslim]

May Allah The Almighty guard us against such disappointment.

Glory be to Allah The Almighty, from Whom none of our affairs is hidden. He knows the treachery of the eyes, and all that the breasts conceal. No matter how much a person deceives and misleads people with his outward appearance, all such deception will be to no avail. Allah The Almighty Says (what means): 

“Indeed, the hypocrites [think to] deceive Allah , but He is deceiving them. And when they stand for prayer, they stand lazily, showing [themselves to] the people and not remembering Allah except a little.” 

(Quran 4: 142)

Moreover, the Prophet  said:

“Allah does not look at your outward appearance or your wealth, rather He looks at your hearts and your deeds.” 

[Muslim]

Surely, people will know the truth soon, either in the worldly life or in the Hearafter. Allah The Almighty Says (what means): 

“As for the foam, it vanishes, [being] cast off; but as for that which benefits the people, it remains on the earth. Thus does Allah present examples.” 

(Quran 13: 17)

One of the greatest reasons behind the absence or lack of sincerity in our actions is seeking worldly gains or aspiring to earn the praise and commendation of people. Ibn Al-Qayyim  said, “Sincerity cannot be combined in the heart together with love of being praised and commended, and greed for what other people have, except in much the same way that water and fire, and lizard and fish are combined.”
He added, “

So if your conscience tells you to seek sincerity, then turn to greed first, and slaughter it with the knife of despair, then turn to the love of being praised and abandon it in the same way those who love the pleasures of this world abandon the Hereafter. If you are successful in slaughtering greed and in abandoning love of being praised, then sincerity will be easy for you. And if you ask, and what will facilitate slaughtering greed and abandoning love of being praised for me? I reply: as for slaughtering greed, then what will facilitate this for you is your knowledge with certainty that there is nothing whatsoever that is desired, except that with Allah alone are its treasures, none possesses them except Him, and the slave is given nothing from them except by Him. As for abandoning love of being praised, then what will facilitate this for you is your knowledge that no one’s praise benefits and adorns, and no one’s dispraise harms and makes one ugly, except the praise and dispraise of Allah Alone.

A Bedouin said to the Prophet  ‘Indeed whoever I praise is adorned, and whoever I dispraise is unadorned.’ The Prophet  said:

‘That is [for] Allah The Almighty [alone].’”

[At-Tirmithi and Ahmad]

So abandon seeking the praise of the one whose praise does not adorn you and whose dispraise does not make you any worse, and seek the praise of the One whose praise is the source of all beauty and whose dispraise results in all forms of ugliness.