Interesting question that was brought up, that I hadn't given much thought about until the other night.
Cleric is next to two enemies. He casts Grace (swift action that doesn't provoke).
Does this mean that his first square is no longer threatened when he starts moving?
Under Provoking an Attack of Opportunity: Moving - Moving out of a threatened square usually provokes attacks of opportunity from threatening opponents. There are two common methods of avoiding such an attack - the 5 foot step and withdraw action.
Grace was always used in thousands of sessions we had before, but always casted with no enemies around to move through enemy squares to prevent provoking.
Because the cleric hasn't started moving yet, does that mean his starting square is still threatened or does Grace now make that starting square exempt?
The spell specifically states your movement does not provoke an AoO.
If moving out of a threatened square provokes an AoO from someone under the spell what purpose does the spell have? The fact that it is your starting square does not make any difference. Moving into a threatened square does not provoke an AoO so how else can you provoke an AoO while moving except by moving out of a threatened square.