Theologically speaking, a disagreement between heart and tongue - or word and deed - about the declaration of faith in Islam is defined as hypocrisy. In the lifetime of the Prophet (PBUH) there existed a group of hypocrites whose traits of characters have been outlined in Ahadith. Humanly it is not possible to perceive malice hidden in one's heart. Even Messenger of Allah (PBUH) hardly knew what lay in the hearts of people because, despite having the exalted status of Prophethood, he was fundamentally a human. Allah, however, had revealed hearts to him. But today, we have no error-free source to pick hypocrites from the ranks of believers. Quite naturally, we fall back on the Hadith which provides us definite symptoms of the character and manners of hypocrites so as to distinguish them from sincere Muslims.
'Ulama' say that there are two aspects of hypocrisy, relating to faith and practice. In the first case, a hypocrite conceals his disbelief in his heart but verbally professes Islam. Anyone who belongs to this category of hypocrites will be, as stated in the Qur'an: "In the lowest depths of the Fire." (4:145). In the second case, a man does have faith in his heart but in practice he portrays the characteristics of a hypocrite, unfortunately a majority of today's Muslims practically behave like hypocrites and possess their propensities. It is this hypocritical attitude and moral deficiencies of Muslims that have degraded them and made Islam unappealing. May Allah put Muslims on the right path!