Good set of answers, to which I'd like to add, if I may:
Managers are keen that the management system is effective, and this is one characteristic that auditors specifically check. To do that objectively, quality objectives have to be measurable. But how to audit quality objectives? How to be sure that, as managers, our measurable quality objectives are useful to our business, its customers and stakeholders? Answer: identify measurable quality objectives that are consistent with the quality policy.
This is why, as someone said, 5.3.c "framework for establishing and reviewing quality objectives" is arguably the most important of the requirements for the policy, and why "meet ISO 9001 requirements" is rather weak as a policy.
A good quality policy is top managememnt's answer to the questions, "What are we doing? For whom? Why?" It's often answered by the mission and vision, which is fine. (It doesn't have to be called the quality policy; whatever it is, it just has to meet the requirements.)
IIRC Disney's Magic Kingdom at Orlando has a quality policy which is something like "Every child leaves the park with a smile on his or her face." (Can anyone point me to a reference for this? I'd hate to have remembered wrongly.)
It's a great policy because it drives a huge range of behaviours. The rides are not only fun, but they're safe. There are amusements while they wait in queues, like meeting characters and watching bands. The park is clean -- kids cry when they step in a nasty mess. You never see the characters out of costume, on a smoking break or gossiping. All the lights work at night. When there's a problem it's dealt with quickly by empowered employees. Keep 'em smiling, all the time.
The behaviours driven by this policy go beyond the rides, to the whole experience - walking in a clean, safe environment, good management of accidents and lost kids, proactive management of safety, fun between one ride and the next, ... It's measurable too: watch 'em leaving the park and count the smiles.
I think a good quality policy is magic, because it drives behaviours both in normal operations, and when there's a problem. It also aligns everyone towards what matters, and renders it all measurable through the quality objectives. Good policies often include something like, "Deliver what the customer wants, in full, on time, and working." (But dressed up in management-speak, of course.)
5.3 is IMHO the most under-rated clause in ISO 9001l; yet in the hands of good leaders, it's perhaps the most powerful.
Hope this helps,
Pat