Do you mean Divine Guardian? It's certainly a disgustingly powerful ability for its position in the tree and might be worth speccing for all by itself.
Edit: Also, I think Beacon of Light might be one of the most OP healing abilities ever. It potentially doubles your healing output, meaning you could place it on the main tank and then raid heal, healing the MT at the same time. Alternatively, you could place it on the OT in a fight like Gruul and then concentrate solely on the MT. It makes me shiver just thinking about it.