[…] someday an enemy bullet will stain you with my blood, (43-46)
As he thinks about how he might die, he imagines getting shot. But the only imagery he gives us is of the suit being stained by his blood. This puts the violence at a distance; it's happening to the suit, not as much to the speaker. There's no mention of pain or injury, even though this bullet leads to his death. Perhaps considering the suit's mortality, which is just a fantasy, is a safe way for the speaker to consider his own mortality, which is far more real.
but perhaps it will be less dramatic simple, (49-52)
Neruda goes on to explain that this more "simple" and less "dramatic" death is one by illness. But aren't some illnesses very dramatic, and aren't some illnesses very complex? It could last years, and require various treatments. It seems that the speaker considers this type of death to be simpler because it isn't the result of violence, even though it may be a more painful way to die. In this way, his attitudes and violence and death are revealed.
and together we will be lowered into the earth. (57-59)
Neruda uses imagery to create a death scene that has a peaceful tone. Together, the two of them are "lowered" into their grave; this could be referencing the slow death of aging that he imagines he and the suit face. Instead of using the word "grave," he says "earth." This reminds us that death is natural, which mirrors the "simple" way of dying that is aging. And the suit is with him; he's not alone. Imagining the suit as his companion forever gives him peace, not fear, even when he imagines being put to eternal rest.