독해문법인데요ㅜ

it is one thing to talk about the problem of the world and quite another to actually try to change things.

해석
세게의문제에대해 말하는것과 상황을변화시키는것은 아주별개의문제이다.
문법적으로설명이안되네요.부정대명사인데..관용표현인가요?