وَإِذَا سَمِعُوا مَا أُنْزِلَ إِلَى الرَّسُولِ تَرَىٰ أَعْيُنَهُمْ تَفِيضُ مِنَ الدَّمْعِ مِمَّا عَرَفُوا مِنَ الْحَقِّ ۖ
Wa-idhā sami‘ū mā unzila ilar-rasūli tarā a‘ayunuhum tafīdu
minad-dam‘i mimmā ‘arafū minal-haqq
And when they hear what has been revealed to the Messenger you will see their eyes overflowing
with tears on account of the truth that they recognize.
(Sūratul Mā’idah, No. 5, Āyat 83)
The verse above was revealed about a certain group of people in Abyssinia, i.e. Ethiopia. When the Muslims first migrated there the King called them to his court. King Negus was a sincere Christian and wanted to know more about the new faith of the people who had sought refuge in his kingdom. He asked Ja‘far bin Abū Tālib the leader of the group of Muslims to recite verses from the Quran to him. When Negus and a group of learned people in the court heard these verses their eyes filled with tears. They recognized the truth from the Lord and wept in acknowledgment.
Tears are very powerful and say a lot about the person who sheds them. It shows that the heart is still soft. It is not hardened and resistant to emotion. The Holy Prophet (s) has said; Crying is from Mercy (Rahmah) and screaming is from Shaytān. (Nahjul Fasaha, pg. 376, H. 1113). He has also said: From the signs of misfortune is a dry eye [which does not weep]. (Tuhafal ‘Uqūl, pg. 47)
Laughing and crying are both tools for releasing emotion. They have an emotional as well as a physical effect on the human being. Just as laughing, it is said, decreases stress, increases immunity and makes a person feel good, crying also has benefits. It de-stresses the body, releases toxins, kills bacteria, soothes emotions, improves the mood and has a generally calming effect.
Tears are a very clear indicator of the powerful emotions that surge inside the human heart. They announce the depth of feelings more effectively than any words can and hence are an immensely strong communicator. It is no wonder that Imam al-Sādiq (a) says: Everything has a value and weight except for tears. A drop of it can put out a sea of fire. (Bihārul Anwār, Vol.90, pg. 331 H. 14).
A believer sheds tears of many types:
1) In the awe of Allah – Nabī Musa (a) was once told by Allah, O Musa, inform your people that nothing is able to get people close to Me like when they shed tears in awe of Me (min khashyati).
2) In regret and repentance – Āyatullāh Khumayni says in his great work Forty Hadith on the exposition on Tawbah: Of the things in respect of which it is necessary for the penitent person to act is taking refuge in the forgiveness of God Almighty and attainment of the state of Istighfār. Openly and secretly, mournfully and pleadingly, in solitude, with lamentation, tears and wails of woe, he should implore the forgiveness of His Sacred Essence to cover his sins and wipe out their consequences.
3) In the love of the Ahlul Bayt (a) – One of the sign of the believers is that they are happy when the Ahlul Bayt are happy and sad when they are sad. Their sorrows grieve their followers. This shows the intensity of their love for them and communicates a more powerful message than a declaration of love.
Let this verse remind you of the importance of tears. God describes it as an indicator of the recognition of truth. When we cry for the Master of the Martyrs, Imam al-Husayn (a), let us understand that it shows our recognition of the truth he stood for and the sacrifices he made for it.
Sources: ‘Allāmah Muhammad Husayn Tabātabā’ī, Tafsīr al-Mīzān
http://www.al-islam.org/forty-hadith-an-exposition-second-edition-imam-khomeini/seventeenth-hadith-repentance-tawbah
http://www.aviny.com/hadis-mozooee/akhlaghi/gerye.aspx