Understand well that the example of the clothing of a person who performs salah, is like the outer skin of a fruit. The body is like the inner skin and the heart is similar to the core and the kernal of the fruit. It is obvious that the object is the core or the kernel. Similarly the aim of this external cleanliness is to purify the heart and to make it effulgent. Perhaps you may doubt, that how can the heart become cleansed by the cleanliness of clothing. Therefore, understand that Allah Ta’laa has kept a special relationship between the inward and outward, due to which, the effect of outward cleanliness definitely has an effect on inward cleanliness. Judge for yourself ! After completion of wudhu, you will find such a feeling of purity and expansion in the heart, which was not found before performing it. It is apparent that this is the effect of the wudhu, which transcends the body and reaches the heart.
Extracted from Tabligh-E-Deen, Imam Muhammed Al-Ghazaali رحمه الله