You are a chosen people, a royal priesthood. 1 Peter 2:9 (NIV)
A truth, rediscovered at the Reformation, is that every believer is a priest of God -- all have direct access to him through Christ. The logical sequence is that all are in full-time Christian service.
Medicine and Christianity are both full-time professions. Although doctors have 'off-duty' times, in an emergency they must be available and, if resuscitation or advice is needed on holiday, they will not withhold their services. This can happen in most unusual ways. The writer when crossing the Atlantic as a passenger on the Queen Elizabeth answered an emergency call and was second signatory to the death certificate of a rabbi who was to be buried at sea before the sunset which heralded the Jewish sabbath. Many will ask our advice simply because we are medical doctors, and after a number of years of 'living and thinking' medicine we often offer advice when it is not asked for.
How about Christianity? We refer to ministers or missionaries as being in 'full-time' Christian service: but we are all servants of God, no less full-time. Have you ever thought seriously about this? Much publicity was given to the actor James Fox who, after a number of years in so-called full-time Christian service, returned to the theatre to serve Christ in this field. Likewise we can serve him in our medical practice. We are called to offer our bodies as sacrifices holy and pleasing to God (Rom 12:1 NIV), and this includes our minds, our thoughts and indeed our work. We are no less in Christian service during a ward round than when worshipping in church.
St Paul (Rom 12:6-8) reminds us of our individual gifts. As the human body is made up of different parts with different functions, so likewise the body of Christ is made up of his servants in every branch of human activity. We should be Christian doctors with equal emphasis on both aspects of our calling.
Further reading: The whole of Romans 12 as a 'job description'.