Sutra:
39. 'Isvaranai ozhinthavarkaL rakshakarallar' ennumidam prapanna parithrANaththilE sonnOm.

Meaning:
That no one other than Sarvesvaran is capable of offering protection was told in the rahasya grantha Prapanna Parithranam.

Sri PBA Swami's Sarartha Deepikai:
Is it correct to say that He is the only rakshaka? Don't we see many people offer protection every day in this world?

The father protects his children; the elder sibling protects the younger; the husband protects the wife; the king protects the people; dEvatas such as Indra, Surya and Varuna also offer protection. This issue has been addressed by Sri Pillai Lokacharya in the rahasya grantha Prapanna Parithranam.

In this grantha, Sri Pillai Lokacharya shows, using many itihAsas and purANas, that limited relations such as mother, father, etc or other dEvatas do not have the power to protect and that He who is the one and true relation to all souls and one who never abandons anyone at any time is the only one who can protect. A few examples from this grantha are shown here.

That brothers are not rakshakas is shown by Vali and Ravana; that children are not rakshakas is seen with Rudra and Kamsa; that parents are not rakshakas is shown by Kaikeyi and Hiranya; that husbands are not rakshakas is shown by Dharmaputra and NaLa. Devas such as Chandra, Indra, etc are defeated by the likes of Hiranya and Ravana and become their slaves and as such they cannot be rakshakas. Brahma is not a rakshaka as Madhu Kaidaba took away the Vedas from him and he suffered (kaNNizhanthEn thanamizhanthEn). Rudra had Brahma's head stuck in his hand and he had to have someone cleanse him of that sin and therefore cannot be a rakshaka.