Why certain lines of the composition are repeated?

The vocalist sings the same words in different Swars or patterns of Swars, as allowed by the Raag framework. This is analogous to taking pictures of an object from various angles or viewpoints. For example, a photographer may take pictures of the Sun at various times of the day from various spots with different levels of exposure. The object of each picture is the same but the discerning eye will notice the differences between two pictures.

The idea is to show changes or variations in order to share the imagination with the listeners and to show the underlying beauty of the Raag. So the singer may change one or two Swars, or change the accent or emphasis on a specific word, or change the Swar pattern leading up to a particular Swar. These are subtle variations, improvisations and ornamentations the vocalist makes to enhance the beauty of the composition.