The pontiff was "informed of the gravity of his situation" and decided to remain in his apartment overlooking St. Peter's Square, said papal spokesman Joaquin Navarro-Valls, breaking into tears at times.
In a spiritual sense, the 84-year-old pope has been preparing the world for such a moment.
As his health has declined in the past decade — sapped by Parkinson's disease and other ailments — his writings and addresses have increasingly dealt with the ethics and morality of the end of life.
The overall message is simple and direct: life holds inherent dignity until the moment of death.
The pope has encouraged research to "enhance and prolong human life" and told doctors it was a moral duty to maintain basic nutrition to patients even in a "vegetative state" — which brought the Vatican in direct conflict with those supporting the decision to remove the feeding tube for the severely brain-damaged Florida woman Terri Schiavo, who died Thursday.
But the pontiff also said it is acceptable for patients to refuse drugs that cause unconsciousness or to reject extraordinary medical measures that would lead to a "precarious and burdensome prolongation of life."
"The fact that he has not gone back to hospital (means) that he is serenely carrying the cross and ready to give up and to say, `It is finished,"' said Irish Bishop John Magi, the pope's private secretary from 1978 to 1982.
John Paul had a full medical team in his Vatican apartment, including his personal physician, two intensive care specialists, a cardiologist and two nurses. The Vatican did not provide a full picture of the medical equipment, but it has been described in Italian media as similar to an ICU unit. His medical team always carries a defibrillator, the electric paddles use to restart the heart.
For years the pontiff has used his deteriorating health as a source of inspiration for followers. Now, his decision not to return to Rome's Gemelli Polyclinic hospital sends another powerful message, said doctors involved with aged and critical care patients.
"He is setting a wonderful example," said Dr. Barbara Paris, director of geriatrics and vice chair of medicine at the Maimonides Medical Center in New York. "Unfortunately, many people, in the United States at least, die in a hospital, not surrounded by family, isolated, or hooked up to machines even when they are deteriorating and there are limits as to what can be done."
The Rev. Donald J. Harrington, president of St. John's University in New York, called the pope's decision "consistent with the way we see many families dealing with death, as a part of life. It is a very human approach."
It's also particularly resonant in Western societies with aging populations but also access to some of the best medical care. The Vatican has not said whether the pope has given instructions for his care if he loses consciousness or is unable to communicate.
Dr. Gene Rudd, associate executive director of the Christian Medical Association, said the pope faced a choice that many critically ill patients must confront.
"There's a point at which the treatment cannot bring about a cure," said Rudd, whose Bristol, Tenn.-based group has 17,000 health care workers. "That's when we switch from curative care to just care."