Pallandu singing is for blessing some one. Normally a younger one will be blessed by an elderly person. Or more learned person will bless less learned person. But if you see periyazhwar has sung pallandu for Maha vishnu. In what way Periyazhwar is elder than Maha Vishnu who has no origin, no birth? Or in what way he is wiser than the omniscient narayana? But his sheer love on god qualified him to sing pallandu. Periyazhwar was given a respectable position by the pandya king. Yet he is a normal down to earth person who is thinking of the lord always. Though he is seated on top of an elephant his thoughts were fixed on namperumal.
When azhwar visualizes lord vishnu with his consort lakshmi, ascended on the garuda, he didnt think that lord should have come down to bless the devotees. But he had a different view. A view of a mother. He thought the lord is so handsome and when he ascends on the garuda, the beauty knew no bounds. He should be protected from the evil eyes. So azhwar sings pallandu thinking that it will protect the lord from the evil. Such an affection periyazhwar had on Vishnu. Even in his other pasurams he use to think him as lord krishna's mother and when he danced on the serpant kalinga, he was very much worried that the poison emitted from the snake should not harm his child lord krishna!