The ending: Humanist v. Christian? (spoilers)
This is an extraordinary film. I caught it last night on TCM and I am astonished that I had never heard of it.
As a child raised in a Roman Catholic family, I visited Lourdes (shortly after the film was shot there). On reaching maturity, I became a humanist and have remained so throughout my life.
Spain's Republicans had good reason to hate priests. Yet Pilar saw beyond her hatred to recognise a man who could be trusted. Francisco's ethical code required him to do the right thing, even though he faced a Facist firing squad for his actions. Manuel Artiguez came to recognise this during their dining-table tete-a-tete and resolved to do the right thing too. If he had killed ViƱolas, Francisco would certainly have been executed. By opting for the traitor, he struck a final blow against Facism before dying a heroic death. But he applied humanist ethics in acting to save the priest.
Why did he come back? To strike a final blow against Facism. To die an heroic death. And (perhaps at the last moment) to save the priest.