For indeed he was sick nigh unto death: but God had mercy on him; and not on him only, but on me also, lest I should have sorrow upon sorrow.
Note 6 at Php 2:27: Some people have interpreted Paul's statements here to say that healing is not a "right" for the people of God, but a gift that is sometimes given and sometimes withheld at God's discretion. That is not what Paul was saying. Healing has been purchased for believers as part of the atonement of Christ (see note 2 at Mt 8:17). The Lord would no more refuse to heal believers than He would refuse to forgive them.
That does not mean that we deserve healing; we don't. It is a gift of God, just as salvation is a gift of God (Ro 6:23 and Eph 2:8). We don't deserve to have our sins forgiven. We cannot demand salvation from the Lord, but we can expect it. Likewise, healing has been purchased for us through the atonement of Christ. Healing belongs to us (see note 4 at Mr 7:27). But it is still the mercy of God that has provided healing, and every act of healing is an act of mercy.
Note 7 at Php 2:27: Paul's statement reveals that the Lord healed Epaphroditus not only for his sake but also for Paul's sake. This illustrates the power of intercession. We can make a difference in the way God deals with another individual. There are many examples of God showing mercy toward someone because of the intercession of another (Ge 19:29, 2Sa 9:1, 1Ki 11:11-13, and 2Ki 8:19).