Please Explain.!?

Question

"Today's student is tomorrow's collegue"

Answer 1

It means that spending your time learning as a student prepares you to be a collegue, or helpful associate, when you are in the working world.

Answer 2

It is a reminder that the person who is in the role of student now, will eventually work with you or for you, possibly even be your boss.

I heard it a lot as a Paramedic, it was a reminder to do a thorough job of training, and to treat the students with respect. That student may eventually show up to treat you or your family- or be in a position to help your career.