One option for a Messaging Provider is a Message Queue, which provides FIFO ordering, i.e. Queue. Why would the ordering of messages be important? I wonder if is it because of the priority of the messages or anything similar to that. i would appreciate if anyone could explain with example.
Your answer is right - logically some operations are interdependent and you must maintain the order of calls.
But I think that there is an even more important purely technical aspect to this that I want to point out: You need to know the order to be able to achieve ACID transactions.
Take the following scenario:
You have a process service that orchestrates 5 other entity/utility services. The process gets triggered and starts executing but 3rd call fails. More often than not it is too expensive to have a common transactional context between services (in order to have 2-phase commit), so the solution is to use Compensation i.e. to call the opposite operations of all services that already did a write operation before the failure. If you cannot guarantee the order of the messages, you cannot possibly know what you should rollback and what not (if you don't explicitly look in the underlying systems and track the change yourself - but this is not a sane approach).
Hope this helps!