Trust in NYS

New York State

Explain this to me like I’m 5:

“I have the limited power to appoint the remainder of this trust to and among my descendants. This power shall be exercised by my Will, and the power granted herein must be specifically referred to in my Will in order to be exercised. This appointment may be outright or in further trust, and need not be equal or proportionate.”

Specifically I guess, why is it referring to the Will. What does the Will have to say or not say?