The difference between (true) khushu`, engendered by faith, and hypocritical khushu` is that the former takes place in the heart for the sake of Allāh and is conduced by veneration, magnification, sobriety, dignity, and shyness. The heart breaks for Allāh, combining dread, bashfulness, love, and shyness with the perception of Allāh’s blessings and one’s own transgressions. This necessarily engenders khushu` in the heart which is then followed by khushu` on the limbs.
Hypocritical khushu`, on the other hand, appears on the limbs; it is a mere pretence, the person affecting something that is not there since the heart is void of khushu`.
One of the Companions would say, ‘I take refuge with Allāh from hypocritical khushu`.’ When asked what it was, he replied, ‘That you see the body humble and submissive while the heart is not.’
The one who has khushu` for the sake of Allāh is a servant in the breast of whom the flames of desire have abated and its smoke has dissipated, replacing radiance in its stead. The blaze of the greatness (of Allāh) has been ignited, and the lusts of the soul have died in the face of fear and sobriety which have, in turn, stilled the limbs and quietened the heart. The heart is content and at peace with Allāh, and it remembers Him; engulfed in the effusion of tranquillity descending from its Lord, it becomes meek and humble (mukhbit). The heart which is meek is the heart which is at peace and rest – for the land which is mukhbit is that which is low-lying onto which water flows and settles. The same applies to the heart: when it is mukhbit, i.e. it has achieved khushu`, it becomes like this piece of low-laying land to which water flows and settles.
The sign of such a heart is that (its owner) will prostrate before Allāh out of magnification and abject humility, broken before Him, never (desiring) to raise his head until the day he meets Him. This is the khushu` engendered by faith.
The arrogant heart, on the other hand, heaves and swells in its arrogance like a fast-flowing river. It is like an elevated portion of the land over which water never settles. This is hypocritical khushu`: the person feigns quietude and affects stillness of limb by way of ostentation. In reality, his soul is raging with lusts and desires; outwardly he displays khushu`, but inwardly the valley serpent and jungle lion lurk between his shoulders, waiting to pounce on the prey.
Notes: Translated from Ibn al-Qayyim, al-Ruh, pp. 346-347