Knowledge of Religion

Rasul Allah (sal Allahu alaihi wa sallam) said: “Whoever Allah wishes well, He gives knowledge of religion.” [Sahih Bukhari]

Eesa (alaihis salam) is reported to have said,
“There are many trees: not all of them bear fruit.
There are many fruits: not all of them may be eaten.
Many, too, are the kinds of knowledge: yet not all of them are of value to men.”

Useful knowledge is like the tree that bears edible fruit. If the knowledge can be used to please Allah, then it is useful. If the utility of that knowledge ends with your death -- in the bigger picture of our never ending existence -- it is useless.