No prayer without purity
لَا تُقْبَلُ صَلَاةٌ بِغَيْرِ طُهُورٍ
La tuqbalu salatun bi-ghayri tuhur.
"No prayer is accepted without purity."
Narrated by Ibn Umar. Sahih Muslim 224
A short reflection
Wudu isn't a formality before the real thing, it is entry into the real thing.