Meaning of the Ayah "Successful Indeed are The Believers"

The one who performs the prayer with all of its arkan (pillars) and wajibat (obligations), but he did not have khushoo' to Allah the Exalted in it, we say he prayed but he didn't pray. (Meaning,) he prayed an outwardly acceptable prayer according to the islamic ruling that we know. However, he did not pray that complete prayer with which the perfect believers have been described in the previous ayah, (The meaning of the saying of Allah): { Successful indeed are the believers, Those who offer their Salah (prayers) with khushoo (tranquility and full submissiveness)} [Al-Mu'minun: 1-2]