One of the most prominent characteristics of believers is the clean, peaceful, trustworthy and loving expression in their eyes. God describes this pleasant and faithful expression in verse: "...You see them bowing and prostrating, seeking God’s good favor and His pleasure. Their mark is on their faces, the traces of prostration..." (Surat al-Fath, 29)
Every person can change his facial expression at will, so it is possible for most people to show an expression of sadness or happiness or anger whenever they wish. However, the spiritual beauty that God describes as "the traces of prostration" can't be achieved through imitation or effort. It can only be achieved through loving God, submitting to the destiny He created, and living sincerely by the morality of the Qur’an; only then does this expression appear naturally on one's face.
About hypocrites, God says in Surah Muhammad, verse 30, "If We wished, We would show them to you and you would know them by their mark..."
It can be understood from this verse that, the face of the hypocrite reflects the insincere, sinister and unclean soul of his. God creates a non-concealable sign on the hypocrite's face, who hides his dishonesty buried in his heart, and thus makes the people Muslims should watch out for known to them.
However, a Muslim himself can't judge a person by saying, "This person is a hypocrite" with certainty because no one has the ability to know the true sincerity and faith of a person. Only God knows. Even when there is evidence against a person, Muslims can only assume that he is "displaying hypocritical characteristics" or "showing signs of a hypocrite." However, the verse "If We wished, We would show them to you," informs us that God can make these people known to His messengers through revelation if He so desires.
While Muslims stand out because of their peaceful, loving and respectful expressions, hypocrites manifest themselves with their blackened countenance corrupted by anger and hatred. They have a disturbing and devilish expression. Sometimes their gaze shows no meaning, sometimes it is full of hatred or discontent, and sometimes it is hostile and offensive. In the Qur’an, one of the most prominent characteristics of hypocrites, their repulsive expressions, is explained in the verse: "[God] knows the eyes’ deceit and what people’s breasts conceal." (Surah Ghafir, 19)
The aim of this devilish expression is to disturb and depress the believers. If the hypocrite can't harm them any other way, his “eyes” are his most effective weapon. God informs us of the immorality of hypocrites and their expressions and the severity of their hatred:
… [they] would almost strike you down with their evil looks when they hear the Reminder. (Surat al-Qalam, 51)
In the era of our Prophet (pbuh), hypocrites were full of hatred and anger because the Prophet and Muslims lived by the Qur’an and preached the faith. They showed this hatred by daring to direct their devilish gaze upon the Prophet.
The characteristics of hypocrites show themselves over the ages, including today, just like God tells us in the Qur’an. Hypocrites, like those who targeted our Prophet to induce distress and unrest, are practicing the same evil acts today toward those who lead Muslims and serve Islam in the most efficient way.