The Reason for Ablution
Man Lā Yaḥḍuruh al-Faqīh|Volume 1|Book 1|Chapter 13
وَ كَتَبَ أَبُو اَلْحَسَنِ عَلِيُّ بْنُ مُوسَى اَلرِّضَا عَلَيْهِ اَلسَّلاَمُ إِلَى مُحَمَّدِ بْنِ سِنَانٍ فِيمَا كَتَبَ مِنْ جَوَابِ مَسَائِلِهِ: «أَنَّ عِلَّةَ اَلْوُضُوءِ اَلَّتِي مِنْ أَجْلِهَا صَارَ عَلَى اَلْعَبْدِ غَسْلُ اَلْوَجْهِ وَ اَلذِّرَاعَيْنِ وَ مَسْحُ اَلرَّأْسِ وَ اَلْقَدَمَيْنِ فَلِقِيَامِهِ بَيْنَ يَدَيِ اَللَّهِ تَعَالَى وَ اِسْتِقْبَالِهِ إِيَّاهُ بِجَوَارِحِهِ اَلظَّاهِرَةِ وَ مُلاَقَاتِهِ بِهَا اَلْكِرَامَ اَلْكَاتِبِينَ فَيَغْسِلُ اَلْوَجْهَ لِلسُّجُودِ وَ اَلْخُضُوعِ وَ يَغْسِلُ اَلْيَدَيْنِ لِيُقَلِّبَهُمَا وَ يَرْغَبَ بِهِمَا وَ يَرْهَبَ وَ يَتَبَتَّلَ وَ يَمْسَحُ اَلرَّأْسَ وَ اَلْقَدَمَيْنِ لِأَنَّهُمَا ظَاهِرَانِ مَكْشُوفَانِ يَسْتَقْبِلُ بِهِمَا كُلَّ حَالاَتِهِ وَ لَيْسَ فِيهِمَا مِنَ اَلْخُضُوعِ وَ اَلتَّبَتُّلِ مَا فِي اَلْوَجْهِ وَ اَلذِّرَاعَيْنِ.
Abu Al-Hasan Imam Ali ibn Musa Ar-Ridha عليه السلام wrote to Muhammad ibn Sinan in response to his questions: "The reason for wudu (ablution), for which it has become obligatory for a servant to wash the face and arms, and to wipe the head and feet, is to prepare to stand before Allah سبحانه وتعالى Almighty, to face Him with one’s visible limbs, and to encounter the noble recording angels with them. The face is washed for the act of prostration and submission. The hands are washed so that one may turn them over in prayer, supplicating with them, expressing hope and reverence, and focusing in worship. The head and feet are wiped because they are exposed, facing all conditions, and do not possess the same level of humility and dedication as the face and arms."
- Ṣaḥīḥ al-Faqīh