Sutra:
179. sEshikku adhisayaththai viLaikkai sEshabUthanukku SvarUpalAbamum prApyamum.

Meaning:
For the soul who is meant to serve Him, making the Lord pleased is true to his nature and is also the goal.

Sri PBA Swami's Sarartha Deepikai:
If a soul does not bring about the Lord's pleasure, then it does not qualify to being a servant. Therefore, doing service makes it that the soul has earned its true nature. Such a service brings about the brightness of His divine face and therefore also satisfies the end seeked by the soul. Thus, this service is worthy of being prayed for eternally.