How does the morale bonus to STR when raging interact with the spell Moment of Greatness when making an attack?
Can you double the +4 morale bonus to STR only on the attack, only the damage roll, both, or either?
The benefit of Moment of Greatness is limited to "one roll or check" per affected creature. Then the creature no longer benefits from the spell.
If the affected creature is benefiting from a morale bonus of any type, it can double that morale bonus on one roll or check, before making the roll. Once an affected creature uses this spell’s effect, the spell is discharged for that subject.
If the attack or damage roll incorporates the creature's Stength modifier in its calculation, and the creature is raging (and has a morale bonus to Strength), then it qualifies.
So you can either:
Suppose you normally rage with a +4 morale bonus to Strength. Then here's the math:
The formula for your attack bonus is usually:
BAB + (STR modifier + 2 from the rage bonus) + misc
and with Moment of Greatness, the bonus effectively increases by +2:
BAB + (STR modifier + 4 from the doubled rage bonus) + misc
If you use a two-handed weapon (let's say a greatsword), then the formula for your damage is usually:
2d6 + (STR modifier + 2 from the rage bonus) x 1.5 = 2d6 + (STR modifier x 1.5) + 3
and with Moment of Greatness, the damage effectively increases by +3:
2d6 + (STR modifier + 4 from the doubled rage bonus) x 1.5 = 2d6 + (STR modifier x 1.5) + 6