The waves, which are a recurrent image in the novel, symbolize the continuity of nature. Against the fleeting, fragile lives of the main characters, the waves that they hear in childhood and then again as they grow older symbolize the unchanging backdrop against which human life is lived out. No wave is exactly predictable or exactly like the one before it, and each one, individually, dissolves in an instance; but the general contours of waves crashing against the shore are unchanging, eternal.
The symbol of the waves has more than one meaning, and this points to a core tenet of Woolf's writing project: experience is subjective, meaning that different people experience the same phenomenon, like waves, in different ways. It is key to her project that the waves have multiple meanings.
This is why Woolf radically rejected the idea of an omniscient narrator in this novel and others: she felt the omniscient form of writing repeated the lie that one person, usually a man, could pronounce Truth. Life, she believed, is far more complicated, far more like the fragmentary, erratic breaking of waves on a shore, and thus to get at this truth, we must gather up the fragments of many people's experiences. This is why we experience the waves through the perceptions of different characters in the novel and at different times in their lives. Rhoda, for example, perceives the waves in Spain at one point in context of the peace that she imagines death brings, imagining committing suicide by walking into the water:
We may sink and settle on the waves. The sea will drum in my ears. The white petals will be darkened with sea water. They will float for a moment and then sink. Rolling me over the waves will shoulder me under. Everything falls in a tremendous shower, dissolving me.
Rhoda is not articulating the truth about waves: she is describing what they mean or symbolize to her.