Sutra:
176. indha chathurththi kainkaryaththai prakAsippikkiRadhu.

Meaning:
The fourth case (caturthi vibhakti) on the nArAyaNa term, speaks of the prayer for service.

Sri PBA Swami's Sarartha Deepikai:
The meaning of the fourth case ("Aya") which is added to the nArAyaNa term is now explained.

This case shows the prayer made to obtain service. The knowledge of the soul's nature leads to obtaining the means. It is appropriate therefore to say that the fourth case, which comes after gaining the means, brings forth the goal of that means which is service.