that1 being the utmost of their knowledge.2 Surely your Lord fully knows those who have strayed away from His Path and He also fully knows those who are rightly guided.
Footnotes
[1]
That is, these people neither know nor can think anything beyond the world and its immediate gains; therefore, it is futile merely to spend time and energy on them.
[2]
This is a parenthetical sentence which has been inserted here as an explanation of the preceding verse.