thiruvadivil – In the matter of His divine form/body.
Just as the first pāsuram was about Śeṣatvam (subservience), and the second pāsuram was about anyaśeṣatva nivr̥tti (removal of subservience to others), this pāsuram is about His assistance through His divine form, as expressed by Āzhvār.
thiru vadivu – Refers to His distinguished form,