I think you are misunderstanding what I'm getting at. Sure people can be very driven or passionate about medicine but the use of the word calling like someone got a sign from god that said become a doctor, well that's a bit much in my opinion. The other definitions psipina used are not what most people mean when they say calling though those definitions do usually provide for the word "driven" or "passionate towards".
If after med school and residency these people still feel it is a calling then I'll believe them but even many of the nontrads on here who've gone back after another more lucrative career ended up saying differently after residency.
Yes, medicine is in turmoil in the U.S., and it is difficult for many to understand why anyone would willingly endure medical education and training because of a sign from God. Here is an inspiring story if you would like to learn more about people who claim to have a calling to go into medicine (in the sense that a religious person would say it). I have included the "History" section, and there is more you can read about this and other stories of physicians who claim to have had a religious calling to go into medicine. Obviously not every "calling" is going to be this dramatic, but in the lives of the people positively impacted it might as well be.
http://en.wikipedia.org/wiki/Christian_Medical_College_&_Hospital
Christian Medical College & Hospital, known simply as "CMC", was founded by Ida S. Scudder, and located in the city of Vellore in the southern state of Tamil Nadu, South India.
History
The idea to start a hospital came in the late 1800's, when Ida visited her medical missionary father, John Scudder, at his post in Tamil Nadu. One night, Ida was asked to help three women from different families struggling in difficult childbirth. Custom prevented their husbands from accepting the help of a male doctor and being without training at that time, Ida herself could do nothing. The next morning she was shocked to learn that each of the three women had died. She believed that it was a calling and a challenge set before her by God to begin a ministry dedicated to the health needs of the people of India, particularly women and children. Consequently, Ida went back to America, entered medical training (practically unheard of for women at that time) and, in 1899, was one of the first women graduates of the Weill Medical College of Cornell University;
Shortly thereafter, she returned to India and opened a one-bed clinic in Vellore in 1900. Two years later, in 1902, she built a 40-bed hospital, the forerunner of today's 2000-bed medical center. In 1909, she started the School of Nursing, and in 1918, a medical school for women was opened. (Men were admitted in 1947). With the training of these women as doctors and nurses, Indian women would now begin to have access to health care professionals. {In 1928 Mahatma Gandhi visited the medical school and appreciated her work.}
In addition to the care of women, Ida Scudder saw the need for bringing health care to the poor, the disabled, and the neglected of India. She traveled regularly to outlying villages, bringing medical care to the doorstep of poor villagers, starting CMC's first "roadside" dispensary in 1916. Over the years, these roadside dispensaries have developed into extensive rural health and development programs that have become internationally acclaimed in the Community Health field. These dispensaries have attracted members of the medical community from around the world, from young medical students to nurses to highly skilled surgeons, to study and contribute their skills.
The 100 years since Ida Scudder opened the first small clinic have seen considerable growth. Today, there are 3,000 outpatients per day, 1,000 inpatients, 55 operations, 22 clinics, and over 30 births every day. Ten bible classes are held each day and 380 patients are visited by a chaplain. In addition, there is the work of CHAD, CONCH, and RUSHA, which go out to the villages and rural areas bringing methods of disease prevention, health care and community empowerment to tens of thousands more. CMC employs over 4300 people today, and is widely acknowledged to be one of the top Medical schools in India.