بسم الله الرحمن الرحيم
Ibn Al-Qayyim – rahimahu Allah – said:
Likewise, from among them [i.e. the causes that alleviate the chest] is turning to Allah – glorified and most high be He – in repentance, and loving Him with all your heart, advancing towards Him, taking pleasure in worshiping Him.
Because there is nothing more relaxing to the chest of the slave than that. To such an extent, that you’ll sometimes find the slave saying: “If I’m going to be in Paradise in state of being similar to this, then in such a case I’ll truly be living a pleasant life”.
Love [of Allah] has an amazing effect in alleviating the chest, bringing about pleasure to the soul and happiness to the heart. None knows this except he who has actually experienced it.
Each and every time the love grows stronger, the chest ends up expanding and alleviating further. It doesn’t become constrained except when [the slave] sees those who are idle and inactive concerning this affair, because seeing them sores his eyes [i.e. upsets him] and mixing with them agitates his soul.
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