Purification

Allah's Messenger  said, The key to Paradise is prayer and the key to prayer is cleanliness (Ablution).

Ablution in Islam is the first step to do before facing the whole face to the presence of Allah the Almighty. Without it a Muslim cannot perform a prayer. 

Ablution is an outward evidence that Islam required its adherents to become pure - inner and outer. The outward purification will continue play its role while on praying where one face is in the presence of Allah. The men who always have contact with Allah are them who have purified hearts. 

But those will prosper who purify themselves,

 And glorify the name of their Guardian-Lord, and (lift their hearts) in prayer. Qur'an 87:14-15