Norm Geras probes the tension between Christian understanding of free will and the Church's command to not commit suicide:
The metaphysical freedom to take one's own life is not worth as much if it isn't one's own to take but under an authoritative prohibition. Furthermore, every other choice in which right is told from wrong by reference to God's will is now equally constrained. If your life isn't yours to take, then presumably it also isn't yours to do with as you judge to be right in other respects. Not only may you not kill yourself because you don't belong to yourself, you may not act according to your conscience when your conscience is in conflict with some putatively God-given rule on other matters. The sphere of moral deliberation and choice that this delivers for the committed believer is significantly eroded; and the image of the free person as morally autonomous and fit to arrive at his or her own reflective judgements is undermined. Is this an intellectually acceptable state of affairs for those attached to the gift, and the value, of metaphysical freedom?
These are deep questions. I find it very hard to believe that the God I believe in would not see a desperate suicide with compassion in the way the Church's dogma cannot. But what the Church rightly intuits is that what is at stake here is not free will to do what you want; it is free will to end free will, to end the mysterious gift of life long before it is over. I distinguish this as well from the suicide of those in desperate pain and no real life yet to live.