We have to acknowledge that we don't 'see' very far yet. There is mystery in healing, as there is in living. We don't understand the mystery of life, nor do we understand a lot about eternal life. However, we know that God gives life, and sustains life. We can learn more about how to co-operate with God, including learning how to pray more effectively, believe more truly, and love more fully.
Healing is complex.
Most healing takes time, but intervention through prayer or medicine can speed up the process, sometimes dramatically. These are inter-related. We are also learning more about blockages to healing such as unforgiveness, unbelief, unhappiness, and unwillingness to yield fully to God. These can be removed in a loving, caring environment. One major discovery in charismatic renewal, and in similar ministries, has been the reality of God's healing grace revealing the Father's love, such as through compassionate prayer in Jesus' name in the power of the Holy Spirit.