Bismillah. We say and repeat the kalima so often that at times, we forget its significance and its power. The kalima is testifying (meaning, as if you witness this fact using your senses) that la ilaha ill-lal-lah: there is no deity/object/thing worthy of any act of worship except Allah.
Recipe for Success
…Say la ilaha ill-lal-lah and you will be successful…
[Excerpt from an authentic narration]
Highest Level of Faith
Eman (faith) consists of 60 or 70 parts, the highest is to testify la ilaha ill-lal-lah, lowest is to remove a harmful thing from a road, and modesty is from eman.
[Reported by Sahih Muslim]
Equivalent of Freeing Noble Slaves
The Messenger of Allaah (S) said: “Whoever says the following in the morning:
‘None has the right to be worshiped except Allah, alone, without partner, to Him belongs all sovereignty and praise and He is over all things omnipotent.’
…has indeed gained the reward of freeing a slave from the children of Ismaa’eel [AS], and ten of his sins are wiped away and he is raised ten degrees, and he has found a safe retreat from the devil until evening. Similarly, if he says it at evening time, he will be protected until the morning.’
[Reported by Abu Dawud, ibn Majah]