Providing medical aid in the war zone was a matter of life and death.

a matter of life and death 是固定短语，意思是"生死攸关的大事；极其危急的情况"。它强调某件事重要到关系生死，必须立刻处理。例句中形容在战区提供医疗援助事关人命，刻不容缓。