The reason behind making dhikr and du’aa following wudu
The Wisdom behind Supplication after Making Wudu`
Shaykh Saalih ibn Fawzaan al-Fawzaan (حفظه الله) said:
“The reason behind making dhikr and du’aa following wudu` (ablution) is to combine both physical and spiritual purity, for wudu` is a means of physical purity, whereas dhikr and du’aa (implying tawheed and tawba) are signs of spiritual purity.
In this way, one becomes in the most perfect state of purity (combining both physical and spiritual purity) and becomes pure enough to be admitted to stand before Allaah in prayer, imploring Him humbly and submissively.”
[Mulakhas al-Fiqh Vol. 1, Chapter 7]