Virtue of Sincerity
Values of deeds vary according to their purposes. The measure of decency and acceptance of deeds depends upon the nobility of purpose and purity from blemishes of cheating, defraud, and hypocrisy. In view of the Islamic Sharia, the only incentive is the intention that stirs the deed. Whenever such an intention is heartily provided to God and purified from the blemishes of showiness, it will be honored by the acceptance of God. Conversely, if cheating and showiness is mixed with the intention, the wrath and refusal of God will befall it. On that account, sincerity is the cornerstone of the beliefs and the factual stipulation that is specified for the validity of deeds. Sincerity, also, frees from inducements and deceptions of the Devil:
He(the shaitan)said, By Your Glory, I shall seduce all of them (children of Adam) except Your sincere servants among them' (38:82-3)."
Obstacles of Sincerity
Since sincerity is the brilliant lodestar that shows the courses of true obedience and honest worship of God, the Devil has used all snares for inducing people through a great variety of deceptive expectations, such as fondness of reputation and wealth, attainment of glory, and seeking for material desires. Sometimes, the devilish inspirations may come in the form of soft, deceptive whispering. Accordingly, one may practice acts of obedience to God with the intention of sincerity, but if he examines them closely, he will find them mixed with showiness. This is in fact one of the most dangerous slips that nobody can evade except the genuine disciples.
It is related that a man said: "For thirty years, I used to offer my prayers collectively in the mosque in the first row. One day, I was late because of something and I had to join the second row. As soon as I stopped, I felt embarrassed. Only then, I discovered that my previous prayers had been my source of pleasure."