In other words it is to believe in Allah and in His Messenger Hazrat Muhammad (pbuh), and not associating anybody or anything else in the worship of Allah, to give Allah an exclusive and pure worship, and not worshipping even Muhammad (pbuh) who is only a Messenger of God and not a god or partner along with Allah. It is about believing firmly in the unicity of Allah and submitting oneself completely to His will.
It is only after one has established himself firmly in the Shahada that one establishes himself in prayer, as a sign of the very submission which he proclaimed, not only openly but inwardly, with all his intellectual faculties as well as his inner consciousness which we usually coined as the mind, as well as with his heart and soul. These three mind, heart and soul intertwined each other in nearly similar significance as these three concerns the spiritual side of the believer, which is beyond his body and carnal passions. If these three as well as his body are regulated in the correct way, then the submission to Allah comes naturally without any clash with external or even internal passions which may ruin his bond with Allah. To maintain his body and soul in harmony with Islam, Salat is thus very important. And the establishing of Salat in the correct way will assure the believer success in this world and the Hereafter.