Wudu is the prescribed ritual whereby filth are cleansed and removed so Allah’s believing slave may stand pure in His presence. The effect of wudu that manifests itself outwardly is the cleansing of the body and the limbs used in the act of worship (salah). The inward effect on the other hand, is subtle, as it has to do with purification of the heart from its sins through repentance. The two aspects of wudu are inscribed in the statement of Allah, Most High:
“Indeed, Allah loves those who are constantly repentant and loves those who purify themselves.” (Surah al-Baqarah 2:222)
wherein He links repentance with purity, and the statement of the Prophet, peace and blessings of Allah be upon him:
“O Allah, make me among those who turn to You in repentance and make me among those who are purified.” (Recorded in Tirmidhi)
wherein He prescribed for us to supplicate to be among the cleansed and among the repentant ones.
Allah therefore, perfected for His believing slaves degrees and layers of purity and servitude (to him); inwardly and outwardly at every stratum; bearing witness that there is none worthy of worship except Allah and that Muhammad is His Messenger, purifies himself from disbelief and polytheism, turning to Him in repentance purifies him from sins, and using water in wudu purifies him from visible filth.
Inner Dimensions of the Prayer by ibn Qayyim al-Jawziyyah Pages 27-28