The statement of Allah; “The Most Gracious (Ar-Rahman), The Most Merciful (Ar-Rahim)” comprises an aspect of servitude to Allah that is exclusive to Him; when the slave of Allah recites it, he testifies to the All-encompassing Mercy of Allah that covers everything and embraces every being; every creature enjoys a share of His Mercy. In reality, it is by His Mercy that His slave stands up (in salah) before Him; it was related in a report that Angel Jibril says every night: “Let so-and-so get up (to pray) and let so-and-so remain asleep.” [Ibn Rajab mentioned this report, others narrate that Allah says every night: “O Jibril, let so-and-so get up (to pray), and keep so-and-so asleep”] It is the Mercy of Allah that puts a person at His service to invoke Him with His divine words (i.e. the Qur’an), beseech His mercy, Kindness and Guidance, and adjure Him to perfect His Grace upon him in this life and in the Hereafter. Indeed, His Mercy embraces all things just like how He embraces all things in His Knowledge, and His praise manifests in all things. Allah said,
“Our Lord! You comprehended all things in mercy and knowledge.” (Surah Ghafir:7)
While, the favoured slaves bask in His mercy, others are deprived from this Mercy as they are expelled from enjoying His exclusive Mercy (i.e. salah).
Inner Dimensions of the Prayer by Ibn al-Qayyim Al-Jawziyyah Pages 38-39