I know exactly what you mean, Maha! One way that we communicate this to first year undergraduate students is to write something like this in the course booklet:

Essential – Be there
You ARE the course! The course happens as we talk, listen, engage and generally do stuff together. It’s important for you to attend – to be with your fellow students – to work together to create the course.
Tip: As the whole course is important, any class missed, for any reason, should be caught up: read your friend’s notes, ask them what happened and why… Keep on top of it from the beginning – you know it makes sense!