Guardian Spirited is a little addon of which the most imporant use is to announce:

• When you cast Guardian Spirit (and on who),
  
• When it procs, thus saving your targets life,
  
• When it fades without proccing.

In addition, it can announce all the other relevant priest spells as well (Pain Suppression, Power Infusion, Mind Control, Shackle Undead, Fear Ward, Silence, Resurrection, Divine Hymn, and Hymn of Hope).

It can announce this to /ra, /rw, /bg, /p, /s, and/or a custom channel. By default, it announce to the appropriate chat (so if you're in a raid, only to /ra and not also in /p).

Optionally, it can also whisper the person you cast your spell on, on all these occations (if the target was an actual person, that is, instead of for example a Mind Controlled mob).