Death is a primary preoccupation of the novel. When Robert Jordan is assigned to blow up the bridge to coincide with the commencement of the Republic's early attack, he knows that he may not survive it. Pablo, Pilar, and El Sordo, leaders of the Republican guerrilla bands, see that likelihood also. Almost all of the main characters in the book contemplate their own deaths. Before the operation, Pilar reads Robert Jordan's palm, and after seeing it, refuses to comment on what she saw, foreshadowing his untimely demise.
Camaraderie and sacrifice in the face of death abound throughout the novel. Robert Jordan, Anselmo and others are ready to do "as all good men should" – that is, to make the ultimate sacrifice. The oft-repeated embracing gesture reinforces this sense of close companionship in the face of death. An incident involving the death of the family of the character Joaquín serves as an example of this theme; having learned of this tragedy, Joaquín's comrades embrace and comfort him, saying they now are his family. Surrounding this love for one's comrades is the love for the Spanish soil. A love of place, of the senses, and of life itself is represented by the pine needle forest floor—both at the beginning and, poignantly, at the end of the novel—when Robert Jordan awaits his death feeling "his heart beating against the pine needle floor of the forest."
Suicide always looms as an alternative to suffering, since likely if captured as prisoners they would be tortured. Many of the characters, including Robert Jordan, would prefer death over capture and are prepared to kill themselves, be killed, or kill to avoid it. As the book ends, Robert Jordan, wounded and unable to travel with his companions, awaits a final ambush that will end his life. He prepares himself against the cruel outcomes of suicide to avoid capture, or inevitable torture for the extraction of information and death at the hands of the enemy. Still, he hopes to avoid suicide partly because his father, whom he views as a coward, committed suicide. Robert Jordan understands suicide but doesn't approve of it, and thinks that "you have to be awfully occupied with yourself to do a thing like that."
The novel explores political ideology and the nature of bigotry. After noticing how he so easily employed the convenient catch-phrase "enemy of the people," Jordan moves swiftly into the subjects and opines, "To be bigoted you have to be absolutely sure that you are right and nothing makes that surety and righteousness like continence. Continence is the foe of heresy." Later in the book, Robert Jordan explains the threat of fascism in his own country. "Robert Jordan, wiping out the stew bowl with bread, explained how the income tax and inheritance tax worked. 'But the big estates remain. Also, there are taxes on the land,' he said. 'But surely the big proprietors and the rich will make a revolution against such taxes. Such taxes appear to me to be revolutionary. They will revolt against the government when they see that they are threatened, exactly as the fascists have done here,' Primitivo said. 'It is possible.' 'Then you will have to fight in your country as we fight here.' 'Yes, we will have to fight.' 'But are there not many fascists in your country?' 'There are many who do not know they are fascists but will find it out when the time comes.'" In the same conversation Robert Jordan is having with the others, he also realizes how there are populist policies right in America, namely homesteading which was widely used by American settlers to settle the West from 1863 onward: "Robert Jordan explained the process of homesteading. He had never thought of it before as an agrarian reform. 'That is magnificent,' Primitivo said. 'Then you have a Communism in your country?' 'No. That is done under the Republic.'"
Divination emerges as an alternative means of perception. Pilar, "Pablo's woman," is a reader of palms and more. When Robert Jordan questions her true abilities, she replies, "Because thou art a miracle of deafness.... It is not that thou art stupid. Thou art simply deaf. One who is deaf cannot hear music. Neither can he hear the radio. So he might say, never having heard them, that such things do not exist."
Hemingway frequently used images to produce the dense atmosphere of violence and death his books are renowned for; the main image of For Whom the Bell Tolls is the automatic weapon. As he had done in "A Farewell to Arms", Hemingway employs the fear of modern armament to destroy romantic conceptions of the ancient art of war: combat, sportsmanlike competition and the aspect of hunting. Heroism becomes butchery: the most powerful picture employed here is the shooting of María's parents against the wall of a slaughterhouse. Glory exists in the official dispatches only; here, the "disillusionment" theme of A Farewell to Arms is adapted.
The fascist planes are especially dreaded, and when they approach, all hope is lost. The efforts of the partisans seem to vanish and their commitment and their abilities become meaningless, especially the trench mortars that already wounded Lt. Henry ("he knew that they would die as soon as a mortar came up"). No longer would the best soldier win, but the one with the biggest gun. The soldiers using those weapons are simple brutes, they lack "all conception of dignity" as Fernando remarked. Anselmo insisted, "We must teach them. We must take away their planes, their automatic weapons, their tanks, their artillery and teach them dignity."
The novel also contains imagery of soil and earth. This imagery appears rather famously at the start of chapter thirteen. Jordan and María have sex in a meadow in the forest. He feels "the earth move out and away from under them." Then afterwards he asks María, "Did thee feel the earth move?", to which she responds affirmatively. Variants of this phrase have become a cultural cliché, often used humorously.