question #1 Sahih Muslim 423, Book 4, Hadith 119 : What is the significance of performing prayer with mindfulness and attention in Islam?

One day the Messenger of Allah (ﷺ) led the prayer. Then turning (towards his Companions) he said: O you man, why don’t you say your prayer well? Does the observer of prayer not see how he is performing the prayer, for he performs it for himself? By Allah, I see behind me as I see in front of me.