It is related that the Prophet, on him be peace, once omitted a verse from the part of the Quran he recited in the course of a ritual Prayer. As he was turning to leave, he said: 'What did I recite?' Nobody spoke, so he repeated the question to Ubayy ibn Kab, may God be pleased with him, who said: 'You recited such-and-such a Sura, omitting a particular verse. We are wondering whether it has been abrogated or taken out.' The Prophet, on him be peace, said: 'Good for you, Ubayy!' Then he turned to the others and said: 'What are we to make of people who come for their Prayers, line up in their rows behind their Prophet, but do not know what he is reciting to them from the Book of their Lord? That is just how the Children of Israel behaved, so God, Great and Glorious is He, spoke to their Prophet through inspiration, saying: "Tell your people: 'You present your bodies before Me and you offer Me your tongues, but you keep your hearts from Me. What you are doing is futile.'"' [Nas-Sahih]
This tradition helps to prove that the fundamental elements in ritual Prayer are humility and conscious awareness, and that merely going through the motions, in a state of heedlessness, has little value for the life hereafter. God knows best. We pray for His gracious help and guidance.
"Inner Dimensions of Islamic Worship" - Imam al-Ghazali