Does it do any good to petition for someone’s healing, like from cancer? The scriptures say if they are ordained to live, they will live, and if they are ordained to die, then they will die (D&C 42:48. So if God has already made up His mind on the matter, what good does it do to pray for someone to be healed?
Yes, we exercise faith and hope when we petition for someone else’s healing and thus this is good.
Remember when the Lord was in the Garden of Gethsemane and the Lord even himself, Luke 22:42, prayed, “Saying, Father, if thou be willing, remove this cup from me: nevertheless not my will, but thine, be done.”
I will answer your question, “What good does it do to pray for someone to be healed?”, if they are already appointed to die? With another question:
What good was it for our Savior to pray for a cup to removed from him, by which the Lord already knew it wouldn’t?
Could one of the reasons be, as found in our Bible Dictionary — Prayer:
“Prayer is the act by which the will of the Father and the will of the child are brought into correspondence with each other. The object of prayer is not to change the will of God, but to secure for ourselves and for others blessings that God is already willing to grant, but that are made conditional on our asking for them. Blessings require some work or effort on our part before we can obtain them. Prayer is a form of work, and is an appointed means for obtaining the highest of all blessings.”