Many physicians acknowledge that they don't heal anyone. If someone has a laceration, a physician can clean and treat the wound, but it is God who actually heals it. Yet, there are certain individuals who God works through, in His time and His way, and most importantly, for His purpose. On this topic, New Advent, the online Catholic Encyclopedia, explains the gift of miracles as follows:
This gift is not given to any created being as a permanent habit or quality of the soul. The power of effecting supernatural works such as miracles is the Divine Omnipotence, which cannot be communicated to either men or angels. The greatest thaumaturgus that ever appeared in this world
could not work miracles at will, neither had he any permanent gift of the kind abiding in his soul. The Apostles once asked
concerning a cure of demoniacal possession: "Why could we not cast
him out? Christ replied, this kind is not cast out but by prayer and fasting (Matt. xvii, 18 sqq.). Eliseus could not raise to life
the son of the Sunamitess with his staff.
The grace of miracles is therefore only a transient gift by which God moves a person to do something which issues in a wonderful
The word "thaumaturgus" translates to wonder worker. The greatest
"thaumaturgus" in history was St. Gregory of Neocaesarea who is commonly referred to as St. Gregory Thaumaturgus. When he was made bishop over Caesarea, there were but 17 people in the Christian community there. Throughout his ministry many miracles took place, all for one purpose: To spread the gospel and bring people to Christ. Upon his death, there were only 17 pagans in Caesarea. An overview of St. Gregory's life can be found here.
God chooses through whom He does His will and for what purpose. Some, at times, find themselves being vessels for the gifts of healing and miracles, but only at the discretion of the Holy Spirit, not the discretion of the individual.