بسم الله الرحمن الرحيم
Ibn Al-Qayyim – rahimahu Allah – said:
Likewise, from among them [i.e. the causes that alleviate the chest] is courage, for indeed the courageous one has an alleviated chest, he is easy going and has a big heart.
As for the coward; he has the tightest of chest among people, having the heaviest heart among them. He experiences no form of joy, happiness, delight and bliss, except for that form that is suited for the beastly animals. As for the happiness of the soul, its delight, bliss and joyfulness then every coward is denied that.
Similar to how it is denied for every stingy person, every person who turns away from Allah – The Sublime and Most High, every person who is heedless towards the remembrance of Allah, ignorant of His – The Most High’s – names, attributes and His religion, having his heart attached to those besides Him.
Indeed this bliss and happiness turns into gardens and a paradise in ones grave, whereas that tightness and confinement turns the grave into torment and imprisonment.
Therefore, the slave’s condition in his grave is similar to the heart’s condition in the chest, whether it is in the form of bliss, torment, imprisonment or freedom.
In addition, no consideration is given to a certain external factor related to this alleviation of the chest, and neither is any consideration given to a certain external factor related to the tightness of the chest. That is because external factors go away once their causes have gone.
So, the only matter that is taken into consideration is the actual characteristic established within the heart, bringing about either it’s [i.e. the heart’s] relaxation or its heaviness, because that is the scale [by which a person’s condition is measured]. And Allah is the one from whom aid is sought.
Source: Ibn Al-Qayyim, Zaad Al-Ma’aad, Chapter: Concerning the causes of alleviating the chest, [of which] complete and perfect acquisition belongs to him [i.e. the Messenger] ﷺ