What's Sincerity? How can we tell when we are sincere? Is there anyway we can measure the level of Sincerity in our hearts?

My computer’s English Thesaurus lists the meanings of Sincerity as: honesty, truthfulness, trustworthiness, genuineness, frankness, openness, candor and innocence.

This to me speaks volumes about the universality of this human quality. Sincerity in its basic form being a common human value that’s shared, appreciated and sanctioned by the human spirit, irrespective of one’s race, tribe or creed. Those of you who are familiar with the life of God’s last Messenger, know how the Arabs of Mecca appreciated Mohammed’s integrity and truthfulness long before he became a Messenger of Allah.

Sincerity in thought, word and deed that in a nutshell is what Islam’s all about; God-consciousness in relation to himself, those around him, and his Maker; all three in a way being interrelated.  

"No man is true in the true st sense of the word but he who is true in work, in deed, and in thought," said the Prophet of Islam.

"Verily, the reward of deeds depends upon the intention and every person will get the reward according to what he has intended." If the intention is to show off then the good deeds are nullified.

The first three people on whom judgment will be pronounced and thrown into the Fire, Muslims are warned, are: a martyr who dies to show off his courage, a person who gives to show off his generosity, and a scholar who learns and teaches to show off his learning. All seemingly good actions, yet because of lack of good intentions on the part of the doers, such good actions become the cause of their doers' downfall.

To stress the importance of Sincerity at all times, the Messenger of Islam said:

"Allah does not look at your bodies and appearances but He scans your hearts and deeds."

While the Muslim is exhorted at every step of the way to give charity, and non-payment of Zakaat (compulsory charity) might even take one out of the fold of Islam), yet the best charity, Muslims are taught, is the one whereby "the giver’s left hand does not know what the right hand gives."

Believers are exhorted to be Sincere at all times, in all their dealings, whether public or private, expecting reward from none but Allah:

"Say: Truly, my prayer my service of sacrifice my life and my death, (all) for Allah, The Lord of the Worlds". ( Quran: Chapter 6:Verse:162)