Sincerity and its benefits

Praise be to Allah, the Lord of the Worlds; and may His blessings and peace be upon our Prophet Muhammad and upon all his Family and Companions.

Sincerity means: "Aiming when performing anything to please Allah, i.e. everything one does is for the Sake of Allah, Who has no partners". People differ in achieving this aim.
Sincerity is one of the most difficult deeds for the person because it protects his soul from the danger of his actions. Sahl Ibn Abdullah Tastiri said: 'There is nothing more difficult for the soul than being sincere' .
Yusuf Ibn Hussain al-Razi said: 'the dearest thing in life is sincerity. I try as hard as I can to remove arrogance from my heart. I feel that a plant of a different colour is growing inside it' .
Indeed, patience and steadfastness help the person overwhelm his own inclinations. Allah Says (interpretation of meaning): {As for those who strive hard in Us (Our Cause), We will surely guide them to Our Paths (i.e. Allâh's Religion - Islâmic Monotheism). And verily, Allâh is with the Muhsinûn (good doers)."}[29: 69]. You should also know that sincerity is one of the pillars that makes the deed valid and reward-worthy. Allah Says (interpretation of meaning): {And they were commanded not, but that they should worship Allâh, and worship none but Him Alone (abstaining from ascribing partners to Him), …}[98: 5]. Al-Nasa'e reported from Abu Umamah al-Bahili that a man came to the Prophet (Sallallahu Alaihi wa Sallam) and said: "What is the reward of a man who fights to get reward but also fame?" The Prophet (Sallallahu Alaihi wa Sallam) answered: "Nothing". The man repeated his question three times and the answer of the Prophet (Sallallahu Alaihi wa Sallam) was the same. And in the third time, the Prophet (Sallallahu Alaihi wa Sallam) added: "Allah does not accept any deed that is not sincerely for Him and for His own Sake" .
So, the doer should be sincere with Allah as it is He Who sustains you.