Since sincerity is a precondition for every action, he mentioned its effect:

Actions are merely propped-up shapes.

Their life-breath is the presence of the secret of sincerity in them.

Actions refer to physical movements or movements of the heart. The shapes are the qualities which the mind fixes. The life-breath ( ruh ) and the secret are lodged in living creatures. Here it refers to that by which perfection is achieved in actions. Sincerity is when the heart is devoted to the worship of the Lord as well as its secret and core. That is the truthfulness designated by being free of strength and might since it is only complete by it, even if it is sound without it since sincerity negates showing-off and hidden shirk . Its secret negates pride. Self-regard and showing off detract from the soundness of the action, while pride detracts only from its perfection.

All actions are forms and bodies. Their life-breath is the existence of sincerity in them. As forms can only abide with spirits since otherwise they are dead and fallen-down, so actions of the body and heart only abide by the existence of sincerity in them. Otherwise they are propped-up shapes and empty forms of no consideration Allah Almighty says, "They were only ordered to worship Allah, making their deen sincerely His, as people of pure natural faith," (98:5) and "Worship Allah, making your deen sincerely His." (39:2) The Messenger of Allah, may Allah bless him and grant him peace, reported that Allah says, "I am the furthest removed from what is associated with Me." The Messenger of Allah, may Allah bless him and grant him peace, said, "That which I most fear for my community is hidden shirk . It is showing off." In one version, "Fear this hidden shirk , It creeps like an ant." They asked, "What is hidden shirk ?" "Showing off," he replied.

In a hadith, the Prophet, may Allah bless him and grant him peace, was asked about sincerity and said, "Not until I ask Jibril." When he asked him, he said, "Not until I ask the Lord of Might." When he asked Him, he told him, "It is one of My secrets which I have entrusted in the hearts of those of My slaves who loves Me. No angel sees it so that he records it and no shaytan sees it so that he can corrupt it" One of them said, "This is station of ihsan : that you worship Allah as if you were seeing Him."

Sincerity has three levels: the level of the common, the level of the elite, and the level of the elite of the elite. The sincerity of the common is to remove creation from dealings with Allah while seeking the portions of this world and the Next, like preservation of the body, money, expanded provision, castles and houris. The sincerity of the elite is to seek the portions of the Next world rather than this world. The sincerity of the elite of the elite to seek to remove all portions. So their worship is to fully realise slavedom and to undertake the requirements of the Lord, or love and yearning for His vision, as Ibn al-Farid said:

My request is not for bliss of the Garden.

     I only desire to see You.

Another said:

All of them worship out of fear of the Fire

      and see salvation as a generous portion,

Or seek to dwell in the Garden

     and to relax in meadows and drink of Salsabil.

I have no opinion of Gardens or Fire.

     I do not seek any recompense for my love.

Shaykh Abu Talib said, "Sincerity with the sincere is to remove creatures from one's dealings with the Real. The first of creatures is the self. Sincerity among the lovers is not to do an action for the sake of the self. Otherwise it is affected by looking for recompense or inclining to the portion of the self. For the unifiers, sincerity is to remove creatures from dealings with of the Real by not seeing them in actions and not relying and relaxing with them in states."

One of the shaykhs said, "Make your actions sound with sincerity and make your sincerity sound by being free from strength and power." One of the gnostics said, "Sincerity is not achieved until people do not see and until he fails to think of people." That is why another said, "Whenever you fall in people's eyes, you become great in Allah's eyes. Whenever you become great in the eyes of people, you fall in Allah's eye." This is when you take note of them and are watchful of them.

I heard our shaykh say, "As long as the slave continues to watch people and have awe of them, his sincerity will never be fully realised." He also said, "Your watching Allah will never be combined with watching creation because it is impossible that you see Him and see other-than-Him with Him." The upshot is that it is not possible to ever leave the self and to be purified of subtle showing-off without a Shaykh. Allah knows best.