It was first obtainable by participating in the second world event, at a cost of 32,000 renown, additionally requiring a runite event token. With the death of Bandos and end of the event, it can now be obtained as a very rare drop from General Graardor and Kree'arra. When received as a drop from the generals, it is automatically learned; it does not drop as an item. When received as a drop, the message You have unlocked the Devotion ability! appears in the chatbox.
Devotion can be very useful in the following cases:
Devotion will block all the attacks from all of the Ascension bosses (including the Lines of Ascension from Legio Quintus).
Devotion will block all the damage from Nex's magic or melee attacks, however it will not protect against the shadow traps, the blood sacrifice attack or the ice prison attack (It will also block the attacks from the minions).
Devotion will block 75% of the attacks in PvP combat.
Devotion will block Dharok's "Give me everything!" attack and also blocks his increasingly damaging attacks as his health decreases.
Devotion used with Deflect Melee blocks Kalphite King's attack AFTER green resulting damage to be 1.
For a while after release, the ability gave full protection of that combat style. As of the patch notes of February 24, 2014, the ability now blocks 75% of the damage in a PvP situation.
When released, Devotion lasted 20 seconds and extended up to 40 seconds. After a hidden update, it was reduced to 5 seconds with a limit of 20 seconds, but due to many player complaints, the patch notes increased the duration of Devotion for 10 seconds.
Originally when this ability was released the cooldown time was 60 seconds. As of the patch notes of February 24th, 2014, this was changed to 90 seconds.