Jesus Christ, whom the Church holds as its founder, instructed his followers to heal the sick. The early Christians were noted for tending the sick and infirm, and Christian emphasis on practical charity gave rise to the development of systematic nursing and hospitals. The influential Benedictine rule holds that "the care of the sick is to be placed above and before every other duty, as if indeed Christ were being directly served by waiting on them". During the Middle Ages, monasteries and convents were the key medical centres of Europe and the Church developed an early version of a welfare state. Cathedral schools evolved into a well integrated network of medieval universities and Catholic scientists (many of them clergymen) made a number of important discoveries which aided the development of modern science and medicine.
Saint Albert the Great (1206–1280) was a pioneer of biological field research; Desiderius Erasmus (1466-1536) helped revive knowledge of ancient Greek medicine, Renaissance popes were often patrons of the study of anatomy, and Catholic artists such as Michelangelo advanced knowledge of the field through sketching cadavers. The Jesuit Athanasius Kircher (1602 – 1680) first proposed that living beings enter and exist in the blood (a precursor of germ theory). The Augustinian Gregor Mendel (1822-1884) developed theories on genetics for the first time. As Catholicism became a global religion, the Catholic orders and religious and lay people established health care centres around the world. Women's religious institutes such as the Sisters of Charity, Sisters of Mercy and Sisters of St Francis opened and operated some of the first modern general hospitals.
While the prioritization of charity and healing by early Christians created the hospital, their spiritual emphasis tended to imply "the subordination of medicine to religion and doctor to priest". "hysic and faith", wrote historian of medicine Ray Porter "while generally complementary... sometimes tangled in border disputes." Similarly in modern times, the moral stance of the Church against contraception and abortion has been a source of controversy. The Church, while being a major provider of health care to HIV AIDS sufferers, and of orphanages for unwanted children, has been criticised for opposing condom use. Due to some Catholics' belief in the sanctity of life from conception, IVF, which leads to the destruction of many embryos, surrogacy, which relies on IVF, and embryonic stem-cell research, which necessitates the destruction of embryos, are among other areas of controversy for the Church in the provision of health care.
Catholic social teaching urges concern for the sick. Jesus Christ, whom the church holds as its founder, placed a particular emphasis on care for the sick and outcast, such as lepers. According to the New Testament, he and his Apostles went about curing the sick and anointing of the sick. According to the Parable of the Sheep and the Goats, which is found in Matthew 25, Jesus identified so strongly with the sick and afflicted that he equated serving them with serving him:
For I was hungry and you fed me, thirsty and you gave me drink. I was a stranger and you received me in your homes. Naked and you clothed me. I was sick and you took care of me, in prison and you visited me ... hatever you did for one of these least brothers of mine, you did for me.