So the bonuses you get with Avenging Wrath and the priest's new talent Guardian Spirit will stack on the target you are healing, and if you have Beacon of Light on top of that its even better.
With Avenging Wrath my Holy Light crit heals are averaging within the 10,000-11,500 range. Combined with Guardian Spirit on the same target, it can reach 15,000-16,000 crit heals.
Guardian Spirit only has a 10 second window so you have a choice of how to make use of this short time. Either hit Divine Favor and go with Holy Shock so Infusion of Light gives you the instant cast Holy Light for quicker procs of Light's Grace. Or Divine Favor and go straight into Holy Light so you get that big 15k crit heal automatically instead of hoping it'll crit after Holy Shock, but you get less heals in the alotted time frame before Guardian Spirit drops. In a well-timed manner, you and the Priest can get a very powerful desperation heal.
Now if you have Beacon of Light and possibly the Holy Light glyph, well you just pulled 30,000 healing in one shot with 10% of the total to 5 others around your target.