In plain words
Not only the holy days of the people of Bhārata, but the holy days of every nation in the world were established to strengthen faith in God, to make the practice of Dharma grow, and to make these firm: the fear of sin and love for merit. Each one, as he keeps these holy days, looking at his own state and circumstances and examining them. These are the days on which each one sees, “How far have I travelled in the effort to turn my life into divinity?”, and sets himself to stride forward.
Sant Tulasīdās has written that in his poem, the ‘Rāmacarita Mānasa’, he composed the story of Raghunātha “svāntassukhāya” (for his own happiness). He did not compose that Rāmāyaṇa, it is said, hoping for the praise of others. Nor was it, it is said, in hope of the praise of the Paramātma; he wrote that great poem for his own joy, only for the contentment of his own Ātma! That is true! People spend their strength and their abilities on such efforts as building a house, doing their work and acquiring property and possessions. All of these are only for their own satisfaction, their own contentment, are they not! The cuckoo's song is not for the praise of others; it is only to show forth its own power and win the happiness of its own heart. The rose blooming and showing forth its sweet scent and its lovely form is ‘svasukhāya’, and nothing else. Even a mother seating her little child on her lap and chattering with it does not do it with the child's happiness in mind; it is for her own happiness: that is the truth. In the same way, all the sādhanas each one performs, arcana, dhyāna, worship and the rest, are solely for the person himself, and not for anyone else. But such sādhanas do not win you Mokṣa, which is the ending of delusion; nor do you gain the eternal Ānanda called svāntassukha. “Na karmaṇāna prajayādhanena, tyāgenaike amṛtatva mānaśuḥ”: not through karma, not through gaining progeny, not through earning wealth is immortality won; it is gained only through sacrifice, so it is declared in the Śruti.
The Onam festival you keep this day brings you this teaching of truth. On this day it is your tradition, is it not, to call to mind the story of how Emperor Bali, at the time of his yāga (the rite of sacrifice), gave three steps of land to Mahāviṣṇu, who had come as one asking for alms in the guise of a brahmin boy; how, when that Vāmana became Trivikrama, Bali saw that there was no room left for the third step, and begged Him to set His foot on his head, and so made his birth worthwhile! This day of the festival of “Onam” is the day on which God, coming down as Vāmana, proclaimed to the world the greatness of sacrifice, the ground of immortality.
There are many noble stories about the land of Malayāḷam (Kerala); from the time of Śaṅkarācārya the tradition has come down of appointing only Nambūdri brahmins from Kerala as the priests (Rāval) who worship Śrīman Nārāyaṇa at the holy place of Badarī in the Himālaya mountains.