Linger with them briefly before their lessons, giving advice to persist (4,3,6)
I believe the answer is:
stay the course
'linger with them briefly before' is the definition.
I don't know anything about this answer so I can't tell whether it can be defined by this definition.
'lessons giving advice to persist' is the wordplay.
I cannot really see how this works, but
'lessons' could be 'course' (a course has lessons) and 'course' is present in the answer.
'persist' could be 'stay' (synonyms) and 'stay' is located in the answer.
The remaining letters 'the' is a valid word which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).
'their' is the link.
Can you help me to learn more?
(Other definitions for stay the course that I've seen before include "reach the end" , "Stick it out to the end" , "Endure to the end" , "Pursue a difficult task until the end" , "Maybe last in battle" .)