يَا أَيُّهَا الَّذِينَ آمَنُوا إِذَا قُمْتُمْ إِلَى الصَّلَاةِ فَاغْسِلُوا وُجُوهَكُمْ وَأَيْدِيَكُمْ إِلَى الْمَرَافِقِ وَامْسَحُوا بِرُءُوسِكُمْ وَأَرْجُلَكُمْ إِلَى الْكَعْبَيْنِ

The purpose of salat (prayers) is to purify a man of all evils. Ablution, or wudu, is the preparation of the body for this religious rite. When a man intends to offer prayers, he first goes in search of water. Water is a great gift of God which is the best thing for washing all the impurities out of man. Similarly, salat is a ‘divine spring’ in which a man bathes and purifies himself of evil emotions and vicious thoughts. Initiating the process of ablution (wudu) when a man puts water on his hands, he is, in effect, praying, ‘O, God! Save these hands of mine from indulging in evil, and let whatever evil deeds I have indulged in through them be washed off.’ Then he rinses his mouth and washes his face. At that time his soul prays silently, ‘O, God! Kindly remove the bad effects of any improper food I have put in my mouth; the evil words I have uttered, and the evil things I have seen.’ Thereafter, when he takes water in his hands and massages his head with his hands, his whole existence is moulded by the prayers, ‘O, God! Wash away the bad effects of the evil ideas conceived by my mind and wrong plans devised by me, and cleanse and purify my mind.’ When he washes his feet, this action of his becomes the entreaty before his Lord, that He may cleanse his feet of the dust of evil and make them (his feet) never tread any path except the path of righteousness and justice. In this way, the whole process of ablution assumes, so to say, the practical shape of the prayer, ‘O, God! Make me a person who turns away from wrongs and one who keeps himself clear of evils.’ In normal circumstances, ablution is enough to create feelings of cleanliness in man, but the state of impurity (resulting from sex) is an extraordinary condition. So, in this state, washing of the whole body (ghusl) has been prescribed. However, God does not like to cause his subjects any unnecessary hardship. Therefore, in case of any practical difficulties in taking a full bath, dry ablution (tayammum) has been declared as sufficient to revive the feeling of cleanliness. The simplicity of the methods prescribed for ablution and bathing is a great blessing of God. In this way physical cleanliness is linked with purity under the Islamic law. In case of any difficulties, permission for dry ablution is an additional blessing, because this saves one from the excesses of which many other religions suffered.

— Source: Tazkirul Quran (Maulana Wahiduddin Khan) via Quran.com (5:6)