Catechism of the Catholic Church

The Holy Spirit gives to some a special charism of healing so as to make manifest the power of the grace of the risen Lord. But even the most intense prayers do not always obtain the healing of all illnesses. Thus St. Paul must learn from the Lord that "my grace is sufficient for you, for my power is made perfect in weakness," and that the sufferings to be endured can mean that "in my flesh I complete what is lacking in Christ's afflictions for the sake of his Body, that is, the Church." (798, 618)