I found this on the elitistjerks priest forum as well as the macro.
Basically you don't need the Revelations talent point. Use of this macro will work even if not specced into Revelations :
/cast [exists,harm] Holy Word: Chastise; [target=mouseover,exists,nodead,help] Holy Word: Serenity
/cast Holy Word: Sanctuary
Tested it, it works.