Sutra:
23. athAvathu anjarththam.

Meaning:
What are the meanings that are to be understood? Those are the five known as Arththa Panchakam. They are: nature of the Supreme, nature of the Jiva, the nature of the means, the nature of the goal seeked and the obstacles to reaching the goal.

Sri PBA Swami's Sarartha Deepikai:
Both the Vedas and their angas profess only five meanings. They are: the nature of the Lord who is to be attained, the nature of the soul that strives attain Him, the nature of the means to attaining Him, tha nature of the goal once He is reached, and the nature of the obstacles to that goal. These are collectively known as the Arththa Panchakam.

As said in the Thiruvaymozhi taniyan "mikka iRai nilaiyum meyyAm uyir nilaiyum, thakka neRiyum thadiyAgith thokkiyalum oozhvinaiyum vAzhvinaiyum Othum kurukaiyarkOn yAzhinisai vEthaththiyal", it is the meaning of this arththa panchakam that is being stressed in Nammazhvar's Thiruvaymozhi as well.

In the Thirumanthra, the praNava expresses the nature of the soul, the nama: expresses the nature of the means as well the obstacles to the goal, nArayaNa expresses the nature of the Supreme, and the chaturti vibhakti (Aya) expresses the nature of the purushArththa. Therefore, the Thirumanthra also stands for the meanings of the Arththa Panchakam only.