What is the reason for not feeling at ease during prayer? And how do I convince a Muslim of its importance?

If the question refers to a lack of khushu' (devotional humility), then there are previous fatwas that have addressed the importance and causes of khushu'. However, if the question refers to discomfort during prayer due to external factors such as heat or fatigue, then there is no blame, and it is recommended to strive to perform the prayer in a manner that enables khushu'. But if the discomfort stems from the prayer itself, this indicates a corruption of the heart and bears a resemblance to Satan, who dislikes prayer. Prayer encompasses the good of this world and the Hereafter; it is the connection between the servant and his Lord. Whoever shies away from it, this indicates a sickness in his heart, and he should review himself, supplicate to his Lord, and be reminded of what Allah has prepared for those who pray and for those who neglect it.