[Khushūʿ (Devout Humility) in Prayer]

Answer (and Allah grants success): Khushūʿ in prayer is the result of preliminaries and qualities that precede it; it does not come about as it should except when these are present:
1. Firm, settled knowledge of Allah. When knowledge of Allah—majestic is His Glory—takes root in the heart, the awe and greatness of Allah dominate a person; he is filled with fear and reverence. When such a knower of Allah comes to the prayer and enters it, the greatness of Allah is awakened in his heart, awe and reverence are stirred, and bodily khushūʿ follows—generally and in detail.
2. Among the completions and perfections of khushūʿ—without which it does not come as it ought—is that the worshiper know the meanings of the remembrances, and what is intended in bowing and prostration.
Proof for what we have mentioned:
 “Only those fear Allah, from among His servants, who have
knowledge.” [Fāṭir:28]
 “O you who have believed, do not approach prayer while you are intoxicated until you know what you are saying.” [An-Nisāʾ:43]
Source : Min Thimār al-ʿIlm wa al-Ḥikmah vol.1