Whoever submits his face to the Lord, and he is testifying the Best Book, then indeed he grasped the strongest Rope that never breaks, and to Allah returns every event.
The Unbreakable Rope is Adhikr as explained in verse 2: 256. Lord taught through His Messenger that the Lord’s Book Adhikr is the Unbreakable Rope extended from Paradise to the Earth. So whoever holds It, he did holdfast the Lord, and is guided into the Straightpath as explained in verse 3: 101. To submit face to Allah means to turn to Allah every time and remember Him always in every conditions i.e. in his standing, sitting, laying, etc. as explained in verses 2: 152 and 3: 190-191. A person is identified through his face, that is why it is told in this verse as: “Whoever submits his face”. See explanation 16: 48, 64, and 30: 57-60.