Redemption is a Prayer that, if active when a player's life points fall below 10%, will heal a number of life points equal to 2.5x of the player's Prayer level. If the healing effect is activated, it causes the player to instantly use up all of his or her Prayer points. The healing does not depend on how much prayer you have left, so it is advisable to use it when your prayer points are significantly low. If a player's life points drop from >10% to 0% in one hit, the healing effect will not activate due to the player dying before they receive the LP boost.
Note: This prayer does NOT heal you in the same way as "Rapid Heal", which accelerates the life point gaining process as long as the prayer is active. Redemption is a one-time healing to a predetermined amount of life points. Redemption only works if you are being attacked or being damaged (poison and disease counts) while already below, or falling below 10% health. If you have less than 10% life points and aren't being attacked or damaged by any means, it will NOT work. The prayer requires one hit splat to activate, regardless of whether the hit splat is damage taken, or a block/miss.
This prayer is used by people scamming and luring in the wilderness. Telling you to bring only one item, then to turn on this prayer and use protect item. You use up all your prayer points and consequently, your protect item is undone and you lose your most valuable item.
Be very careful when using this prayer in the wilderness as it will drain ALL prayer points and disable Protect Item upon effect.