This is an article written by a good friend of mine ☺☺☺
 
Bismillah

Be aware O reader 'may Allah have mercy on you', it is obligatory upon you to treat the matters of the heart with much importance and care, constantly keeping its state in check, cleaning it from impurities and diseases,thus preventing its death, as it has been said by the scholars,the heart occupies a great position over the other parts of the body.

The prophet صلى الله عليه و سلم said "Indeed there is in the body a lump of flesh,if it becomes sound,then the whole body is sound, and if it gets corrupt, the whole body gets corrupt. Indeed it is the heart." —Bukhari and Muslim.
     Al Haafidh Ibn hajar رحمه الله said: The heart has been singled out for this because it is the leader of the body and through the purification of the leader, the subjects become purified and with his corruption,they become corrupted.

The scholars have made us understand: من عرف قلبه عرف ربه
"He who knows his heart,knows his lord",and as Ibn Qudaamah mentions,'knowing the heart is an integral part of the religion and a basis for those who seek the right way to Allah'..
    Thus this was the understanding of our pious predecessors as sheikh muqbil said: 'By Allah for our bodies to have diseases is more beloved to us than for our hearts to die',and May Allah have mercy on Ibn Al qayyim as he mentions;'A real man fears the death of his heart not the body' and 'The slave is not afflicted with a punishment greater than the hardening of the heart and being distant from Allah,for the heart was created to melt the hardened heart.The most distant heart from Allah is the heart which is hardened,if the heart becomes hardened,the eye becomes dry.
        In the book mukhtasar  minhajul qaasideen,Ibn Qudaamah رحمه الله states:“The heart is like a fort and the devil is like an enemy who seeks to enter this fort to own and control it.The best way to protect a fort is to safeguard its gates.”

SETTING RIGT THE AFFAIRS OF THE HEART
أَلَمْ يَأْنِ لِلَّذِينَ آمَنُوا أَنْ تَخْشَعَ قُلُوبُهُمْ لِذِكْرِ اللَّهِ وَمَا نَزَلَ مِنَ الْحَق

As Allah says in the holy Quran
"Has not the time come for the believers that their hearts should be humble for the remembrance of Allah and that which has been revealed of the truth..[Hadid vs 16]
   Ibn Al qayyim said,"The keys to the life of the heart is in reflecting upon the Qur'an,being humble before Allah in secret and leaving sins.
  And here the criterion (the qur'an) had been mentioned as it encompasses complete guidance by which the slave would attain success, and imam muhammad ibm uthaymeen رحمه الله said: “The best advice that can be given for healing the heart is to pay attention to the Qur'an”
leaving sins and seeking forgiveness –
"When a servant commits a sin, a black spot appears on his heart,and if he seeks forgiveness this black spot is removed, and if he returns to sin,the black spot grows until his heart becomes black.– Muhammed صلى الله عليه و سلم"
Making regular istigfaar helps purify the heart,and man is prone to mistakes and errors as verily he has been created weak.It has been reported by muslin that the prophet peace be upon him said; I seek forgiveness hundred times a day.
If this is the case with the best of mankind, what about us??!!.
May Allah rectify our affairs

KINDS OF HEARTS —Ibn Al Qayyim رحمه الله
The hearts of man can be divided into two kinds,the first of which is the heart of those who incline to The Beneficent, which is the source of brightness,life,happiness, pleasure, delighted blessings. The second one is the throne of the devil where narrowness, darkness, death, sorrow,distress and grief are settled therein,this heart is obsessed by sorrow for the past and grief & distress for the present
At tirmidhi and others narrated, “The prophet said 'If the heart is overwhelmed by the brightness(of faith), surely it will be opened and delighted.'They said; O messenger of Allah, what is the sign in that?,he replied 'Resorting to the  eternal dwelling (I.e Paradise), being averted from the dwelling of deceit (I.e the worldly life),and being prepared for death before its arrival.”
In brief the brightness ,which overwhelms the heart as the impact of being close to Allah, the Almighty and obtaining his blessings of serenity and guidance. This feels the heart with.pleasure, while lacking such feelings that are from knowing Allah and loving him, makes it a gloomy and narrow place.