Sutra:
144. charaNau - thiruvadigaLai.

145. iththAl sErththi azhagaiyum upAya pUrththiyaiyum sollugiRadhu.

Meaning:
144. The term "caraNau" means the divine feet.

145. This term, which is in the dual case, shows the beauty of the togetherness of His lotus feet, and the completeness of the means.

Sri PBA Swami's Sarartha Deepikai:
The next term is "caraNau", whose meaning is, the divine feet.

Because this term is in the dual case, it means a pair of feet. It speaks of the beauty of the two feet being together, looking like two beautiful lotuses kept next to each other ("iNaith thAmarai adi empirAn").

It also speaks of the completeness of the means. How is that? Even in places where the singular case is used, it can mean the many, using the case of "jAtyEkavacanam" (a singular representing a whole class). And in places where the plural case is used, it can mean the singular, using "pUjAyAm bahuvacanam" (using the plural to show respect) and "Atmani bahuvacanam" (using the plural to refer to one's self). Using the dual case however, does not allow the singular or the plural cases. Therefore, the pair of feet being the means, does not tolerate anything else as additional means. Thus, the caraNau term speaks of the completeness of the means.