This is according to Ayatollah Mohammad Baqer Tahriri, director of Marvi Islamic Seminary in Tehran, who in a speech elaborated on the manners of reciting the Quran, excerpts of which are as follows:
In Hadiths there is the talk of Huzn (sadness) and also crying when reciting the Quran and this Huzn is the result of humbleness and Khashiyat (fear of God). Khashiyat may make one cry if one realizes the greatness of God, the Al-Mighty.
In reciting the Quran there is a kind of concentration on connection to the Alam al-Ghayb. This kind of attention is important. We see that when great men of God recited verses of Bisharat (good news) in the Quran, they became happy, because faith is manifested here.
When one sees what blessings God has considered for the faithful, and when one reads the Quran and considers himself worthy of those blessings, he feels happy.
On the other hand, when one reads the verses of punishment, he becomes sad as he considers the possibility that he may also be punished.
So the Quran is a truth every stage of which makes the faithful move, whether moving forward or moving toward ending unfavorable things that could bring punishment.