SURAH AL-BAQARAH: 277

اِنَّ الَّذِيۡنَ اٰمَنُوۡا وَعَمِلُوا الصّٰلِحٰتِ وَاَقَامُوا الصَّلٰوةَ وَاٰتَوُا الزَّكٰوةَ لَهُمۡ اَجۡرُهُمۡ عِنۡدَ رَبِّهِمۡ‌ۚ وَلَا خَوۡفٌ عَلَيۡهِمۡ وَلَا هُمۡ يَحۡزَنُوۡنَ‏۔

"Surely those who believe and do good deeds, establish Salah and Zakah, have their reward with their Lord, and there is no fear for them, nor shall they grieve."

This verse mentions the great reward of internal peace and comfort that awaits the truly believing and practicing Muslims, who are steadfast in Salah and Zakah. The Arabic word "خَوۡفٌ" refers to anxiety and worry about something untoward happening in the future, and the word "حزن" refers to sadness and grief about a loss event. A person who is free of these two emotions enjoys true bliss and happiness. (Ma'ariful Quran)

Hazrat Sufiyan Suri REhmatullah Elaih, who was one of the great saints of his time, used to say that if kings became aware of the inner peace and tranquillity of  Ilm (knowledge), of His Ibadah (acts of worship), and of His Zikr (remembrance) that Allah Ta'alah has bestowed upon us in our hearts, as His blessing, then they would descend upon with us with drawn swords insisting that we hand this peace and tranquillity over to them. 

These days people are afflicted by all sorts of worries, anxieties and mental distress. They try to get rid of it through all sorts of treatments, and still their worry and sadness does not go away completely. In Quran Karim Allah Ta'alah has promised Momineen (people of faith) and Saliheen (virtuous people) again and again that they will neither have anxiety about the future, nor sadness about the past. It does not mean that they do not come across worrying or sad situations. What it means is that once someone places his happiness in Allah's will, in that they are happy with whatever Allah decides for them, then even if they experience adverse circumstances in life they may feel biological anxiety and sadness, but their heart and mind are happy with whatever Allah Ta'alah has chosen for them. A person should trying acting on these verses even if as treatments, he will then InshaAllah experience such peace in his heart that he will get the blessing of وَلَا خَوۡفٌ عَلَيۡهِمۡ وَلَا هُمۡ يَحۡزَنُوۡنَ‏ in this world.