A conditional expression meaning “unless (something is done), (something) won't happen / can't be done.” It is used with a negative verb clause.
説明がないことには、参加を決められない。
Without an explanation, I can't decide whether to participate.
証拠がないことには、有罪とは言えない。
Unless there is evidence, one cannot say someone is guilty.
お金がないことには、留学するのは難しい。
Unless you have the money, it's difficult to study abroad.