Due to the sterility and poverty [of indolence, disaffection, idleness etc] that the hearts and souls endure time and time after, the invitation [to salah] is renewed five times a day. However, the Mercy of Allah necessitated that a gap of time pass between each invitation so that the invitee is constantly calling for the rain from the One in Whose Hand is the water to quench the hearts, and beseeching the clouds of His Mercy to have their water descend upon his heart in order that the trees of man and the harvest of insane, growing from this divine Mercy [of the prayer], do not dry out. The essence of these plants maintains their survival in his heart and in his soul; therefore the heart of the slave of Allah continues to implore in humility for the rain to fall upon his heart from his Lord to invoke Him to relieve his heart from drought and thrust. This truly for the slave of Allah is the way of life.
Indeed, the drought of hearts is heedlessness, but as long as the slave is indulged in the remembrance of Allah and constantly turning to Him, the rains of His Mercy will shower his heart abundantly. As soon as he becomes heedless however, drought shall strike his heart and the damage caused will be according to the degree of his heedlessness. This is because when inadvertency dominates and overwhelmed the heart, its land becomes lifeless; it shall produce no harvest for reaping, and the fire of desires will scorch it from every side, leaving the land bare after it had once been rich with every different kind of vegetation. Nonetheless, as soon as the rains of Mercy fall upon the heart of the slave of Allah, the land of his iman and deeds quivers, and turns fertile, causing every lovely kind to grow thereon, sustained and nourished by the life-giving water. When the land is deprived of water, the branches and leaves of its flora wither away, becoming fruitless; even the branches are bereft of benefit as they become rigid and fragile.
At this juncture, the wisdom of the One overseeing this garden dictates having these dried trees cut and making its wood a fuel for fire.
Inner Dimensions of the Prayer by Ibn Qayyim Al-Jawziyyah Pages 19-20