Sutra:
163. ivanarththikka vENumO? Sarvanjan ivan ninaivaRiyAnO vennil.

164. ivan pAsuram kEttavARE thiruvuLLam ugakkum.

Meaning:
163. Does the chetana need to pray? Will not the all- knowing Lord know what the chetana needs and give that?

164. (This is true; but) When the chetana opens up and asks for what he wants, His divine heart will be pleased (therefore, the chetana should pray).

Sri PBA Swami's Sarartha Deepikai:
As said by Azhvar "uLLuvAruLLiRRellAm udanirunthaRithi", He knows the innermost thoughts of all chetanas. Being that the case, does the chetana need to pray to Him? Isn't he all knowing and therefore know the chetana's wish?

When the chetana, who for countless time has been seeking other goals and not showing any interest in this highest of goals, develops a taste for it and asks for it, His divine heart will be pleased. This is the reason for making this prayer. This is similar to the great pleasure that develops in a mother's heart when her child who has been sick and unable to eat, comes out of the sickness, becomes hungry and asks for food.