"Not only is suicide a sin, it is the sin. It is the ultimate and absolute evil, the refusal to take an interest in existence; the refusal to take the oath of loyalty to life. The man who kills a man, kills a man. The man who kills himself, kills all men; as far as he is concerned he wipes out the world. His act is worse (symbolically considered) than any rape or dynamite outrage. For it destroys all buildings: it insults all women. The thief is satisfied with diamonds; but the suicide is not: that is his crime. He cannot be bribed, even by the blazing stones of the Celestial City. The thief compliments the things he steals, if not the owner of them. But the suicide insults everything on earth by not stealing it. He defiles every flower by refusing to live for its sake. There is not a tiny creature in the cosmos at whom his death is not a sneer. When a man hangs himself on a tree, the leaves might fall off in anger and the birds fly away in fury: for each has received a personal affront. Of course there may be pathetic emotional excuses for the act. There often are for rape, and there almost always are for dynamite. But if it comes to clear ideas and the intelligent meaning of things, then there is much more rational and philosophic truth in the burial at the cross-roads and the stake driven through the body, than in Mr. Archer's suicidal automatic machines. There is a meaning in burying the suicide apart. The man's crime is different from other crimes--for it makes even crimes impossible."
Without commenting on Chesterton's view of suicide, I will add some observations based on my recent work on Gregory of Nyssa. For Gregory, all sin is the active choice of non-being instead of being. In view of this understanding of sin, suicide becomes not the greatest of sins, as Chesterton suggests, but merely the physical acting out of what is already a metaphysical direction in every sin. Sin is the choice of death, of more than death, of descent into non-being altogether. To choose to kill oneself is, at least in the philosophical sense, merely the playing out of the drama of sin up to its inevitable conclusion.