The easiest way to discern the two are in the person they are trying to protect.
A professional association works to protect the interest of their members whereas a regulatory body works to protect the public.
Professional associations provide their members (therapists or other) with networking and professional development opportunities; they can offer discounted rates on professional insurance and give members access to courses, information on the profession and more. It is voluntary for members to be part of professional associations.
Regulatory Bodies protect the public. You! They work to make sure professionals are working ethically and not abusing their power or acting out of good faith. They regulate the work we do to ensure the safety of the consumer. They make sure that the practice of psychotherapy is safe and ethical and that we are following rules to ensure that it continues to be that way. They want to make sure you are getting the best quality of service and if you are not, they want to be there to help you and take your complaints.
Why does this matter? Knowing what association and regulatory body your helping professional is a part of can help you protect yourself.
Hope that clears things up!
The Collective Team