One of the reasons why heart fails to extract any happiness from life is jealousy. Jealousy is such a moral disease that it does not only takes contentment away but also it has the strength to make a pious man, a devil-natured one.
Prophet Muhammad (peace and blessings be upon him) was quoted by Abu Hurairah as saying,
"Allah does not look at your bodies or possessions, but He looks at your hearts and actions."(Muslim)
Our body or what we have cannot make any difference but the only thing that can make difference is the heart, the way we think and deal with other. If there is some illness in the heart, the whole body will suffer but if the heart is contented whole world will look better. Our wealth or riches, our complexion our language even our degrees cannot save us if we are not good morally. And to be good morally needs a good heart.
ALLAH swt says in Quran: (Ash-Shu`araa' 26:88-90)
“The Day when neither wealth nor children can help, but only he (will prosper) that comes before Allah with a sound heart. To the righteous, the Garden [Paradise] will be brought near.”
On the Day of Judgment, we will be judged not by our wealth or our family or anything that has made us proud or happy in the eyes of this world, but the only thing which will be judged will be how we were by heart i.e. by nature. The verse quoted above says that righteous are those people who have sound hearts, mean in whose heart there is no jealousy, no grudges and no hatred for others.
It is jealousy that leads to anaad and hatred. Jealous people do not think for a second about ALLAH all they care about is how to make the person suffer they do nto like because he has something which they do not have. If we find someone having something better than us, then we should pray for his happiness and if we really want that, the best thing to do is to pray for it. The worldly gain is too little to fight for. The real thing is our akhirah, the life which will never end, and which can be good and worst based upon our deeds in this world.
Those deeds which are done to show world that we are pious are soulless and will not do no good, but those deeds which are done keeping in mind the pleasure of ALLAH swt are the one which will be counted and will earn us jannah, the eternal place for the believers.
Qaf 50:31-35
“And the Garden will be brought nigh to the righteous, no more a thing distant. (A voice will say,) "This is what was promised for you, for everyone who turned (to Allah) in sincere repentance, who kept (His Law), who feared (Allah) Most Gracious unseen and brought a heart turned in devotion (to Him): Enter you therein in peace and security; this is a Day of Eternal Life!' There will be for them therein all that they wish, and more besides in Our Presence.”
Jealousy does not only bring hatred but also leads to deceitfulness and hypocrisy. And such people are the worst people because they have the worst type of heart. Prophet Muhammad s.a.w.w described the types of heart as follows:
"There are four types of hearts: a pure heart that shines like a lamp, the covered up and closed heart, the upside down heart and the mixed up heart. The pure heart is that of the believer. The covered up heart is that of the non-believer. The upside down heart is that of the hypocrite who knows and then denies. The mixed up heart is that in which there is both faith and hypocrisy. The example of faith in it is like a small plant that grows with good water and the example of hypocrisy in it is like a wound that grows with pus and blood. So whichever grows bigger takes over the heart." (Ahmad)
Strive for the bright heart, the one which has fear of ALLAH and love for Him and His beloved prophet Muhammad s.a.w.w.