Read the following passage:
'The old lighthouse stood on the cliff's edge, a solitary sentinel against the raging sea.
For a hundred years, its beam had cut through the darkest storms, a steadfast guide for sailors.
Though its lamp was now electric and its keeper long gone, the townspeople still spoke of it with a reverence usually reserved for ancient heroes.
They said it had a spirit, one of resilience and unwavering duty.'
What is the main idea of this passage?
