In plain words
“Since this matters more than every other festival, go to your in-laws' house, O new bridegroom!”
Within a family we live far apart for a long time, so they made this a custom by which all the members of the family, new sons-in-law included, are together happily once a year. When the son-in-law came home, the villagers, the household and even the father- and mother-in-law would welcome him with great joy. In those days the wife's younger sister would tease the newly married brother-in-law in all sorts of ways, they say!
“Your darling sister-in-law will chat with you, your elder sister-in-law will banter with you at every turn, the villagers will honour you with great fondness, even your father-in-law will wait on you hand and foot; go to your in-laws' house and come back, my dear.”
With these words his parents would send him off, they say! That is to say, it is this Sankrānti that gives the unity of the family; the union of the jīva with Brahman; a relationship that is divine, noble, new and natural; the responsibility of action, that we must practise as our duty; the sun's teachings that you must become heroes of action; and this divinity, so great a sacredness, which teaches that steadfastness in karma is man's steadfastness in Dharma.
Today people make do with mere prasāda of sesame and jaggery mixed together; failing to recognise the inner meaning, they make pongal, gorge themselves, and delighted that this is Sankrānti, they sink into darkness without a ray of krānti. Why did they make this pongal? It could be made at any time! Why should pongal be made only for this festival? In those days the harvests were very plentiful. So they cooked pongal, gave it to the cattle, and sprinkled that prasāda over all the crops. On the third day they decorated all the cattle, led them in procession through the streets and shared their joy with all the villagers.