Rationale: Ironskin just isn't very useful. It gives a small-ish boost to AC at a level where AC's importance is in decline. Ardent Faith provides a useful defensive effect, and comes in a little earlier. Its main drawback is that it has a high mana cost and relatively low duration, but I believe it's a lot better than the why-are-you-practicing-this Ironskin.

The helpfile, since we're having a wee technical difficulty with those right now:

Ardent Faith
Syntax: commune 'ardent faith'

Drawing upon their devotion to their higher power, a healer can find
the will to press on despite grievous injuries. This focus manifests
itself in an ability to mitigate the lasting effects of bodily
maledictions received while under its effect. The effort required
to bring forth this supplication is considerable, owing to the
mental intensity involved.

valguarnera@carrionfields.com