The best lesson to draw from the case of Terri Schiavo is the importance of having a living will, said Catholic Bishop Donald Wuerl of Pittsburgh.

Not only should loved ones be given written instructions on what you want and don't want depending upon your medical condition, but you should give power of attorney to a person you trust to carry out your wishes, Wuerl said.

"If you are Catholic or have strong faith convictions, that moral frame of reference should be what guides you in filling out your living will and in your power of attorney," he said.

"Remember, it is the person who has to apply these principles. It is up to the person's conscience. All the church can do is provide the principles."

Two key principles should guide Catholics, he said. One is that they are not required to undergo "extraordinary" medical procedures to stave off death. That means they can elect to forgo or stop a ventilator, dialysis or even a feeding tube, he said.

"The problem becomes when you haven't left any instructions and someone else is trying to figure out what you would want," he said.

But while it is legitimate not to interfere with death, another key principle is that no one should ever do anything to deliberately cause death.

Schiavo's parents argue that she was not dying before the tube was removed - and that it was removed precisely in order to kill her. Wuerl was hesitant to say what kind of advance directives Terri Schiavo might legitimately have left.

"In the Schiavo case we simply don't know. There are conflicting stories about what exactly her capacity is," he said.

The Schiavo case is part of a much larger conflict between what Pope John Paul II describes as the "civilization of love" and the "culture of death," he said. While a civilization of love cares for its weakest members, the culture of death "sees death as an easy solution," he said.

The grand question in the Schiavo case is, "Do we appropriate to ourselves the power to determine who will die, and when?" he said.