Why doesn't this macro work?

[Adreaver-undermine (Adreaver)]

No. This was answered above.

@Adreaver-undermine

3. Macros - What can they not do?

Macros cannot make smart decisions for you. They can’t cast spells based on cooldown, or check if a buff is active, or magically fit all your abilities onto one button.

You can make a macro that will cast Flash of Light, but will cast Word of Glory when you hold shift. You can make a macro that will cast Word of Glory, then Flash of Light. You can’t make a macro that will miraculously decide for you whether or not you are able to cast Word of Glory and then choose the appropriate spell.