Why is it obligatory during wudū to specifically wash or wipe only four parts of the body – the face (including the mouth and nose), hands up to the elbows, head (including the ears), and feet?
Some scholars say that one possible reason (or wisdom) is that these are the parts of the body we sin with the most. So when we wash these parts of the body, we are purifying them from sins, which fall off with the water. The Prophet ﷺ said, “Whoever performs wudū perfectly, his sins will depart his body, even from under his nails.” (Muslim)
Keeping this in the back of one’s mind while performing wudū helps one to perform it perfectly, and perfect wudū prepares one to be in the right state of mind for Salāh.
Whatever the reason, these are the parts of the body we’ve been instructed in the Qur’ān to wash (Sūrah 5:6). But every command of Allāh contains great wisdom.