For the important of ASEAN legal personality concept that is ASEAN it has legal so legal has permission to do, Further more legal personality means ASEAN has to be recognized in domestic law in the term of ASEAN law to Domestic law
How to describe it is law of ASEAN have to be respected in national law for the example MRA in ASEAN this is mutual recognition arrangements that government have to provide place for MRA implementation.
For another supporting legal personality concept it had permission to do activity in international community, it can be a legal person that has a power to negotiation in that way, it can protection like a another countries can’t threaten then.