Require (something) because it is essential or very important
Circumstances in which something is necessary, or that require some course of action; necessity.
Have a desire to possess or do (something); wish for.
A lack or deficiency of something.
The dictionary might say they are synonyms, but in reality the two words mean very different things to people. You friend might need to stop drinking every time she hits a bump on the road, but what she wants is for someone to help her through her problems. Your spouse might need to stop eating fried stuff and watch his weight, but what he wants is your support to help him stop. Your customer might need a complete overhaul of his compensation planning process but what he wants is a smart and painless way of doing it without having everyone up in arms.
You might know what is needed, and you have a swanky need-gap analysis presentation all wrapped up and ready to go.
The question is can you deliver what your customer wants?