The importance of the illimba tree in this book is that it marks the place and also the moment when Sophie Mol drowns and dies. It is when Sophie Mol leads her Indian cousins, Estha and Rahel, on her trip to run away across the river that tragedy strikes, as the boat is upturned when it hits a piece of floating wood and Sophie, who couldn't swim, drows, whilst her cousins swim easily and make it to the shore. Note how this is reported by Roy:
"Sophie Mol? She whispered to the rushing river. "We're here! Here! Near the illimba tree!"
On Rahel's heart Pappachi's moth snapped open its somber wings.
The short sentence of "Nothing" serves to emphasise the terrifying silence that Rahel felt, and this is followed by a reference to the moth as a symbol of fear as Rahel begins to understand what has happened and how Sophie has died. The image of the moth snapping open its wings mimics the sound of Rahel's heartbeat as she goes through the moment of terrifying realisation of precisely what has occurred. The significance of the illimba tree is therefore shown through the way that it is a marker of the precise moment that changed the life of the twins so drastically, as it was Sophie's death that set everything else in motion, and causes massive, unforeseen consequences that would end their life as they knew it.