2 Peter 3:9:

The Lord is not slack concerning his promise, as some men count slackness; but is longsuffering to us-ward, not willing that any should perish, but that all should come to repentance.

See also:

The Baseball Diamond of Healing
The SAVED Test
Healing and the Last Days
Healing and Repentance
Objection: We Cannot Demand Healing from God Because God Is Sovereign
Objection: Sickness, While Unpleasant, Is Used by God to Build Character