By touching them, those blessed by the world will receive the gift of life anew should they stumble and fall.
此句，句末黑体部分是省略了 if 后的倒装句，等于 if they should stumble and fall. 但不是“虚拟语气条件句”，而是 “should 的推定式” 用法。简单地说，should 有一特殊用法，表示说话人对将来发生之事不确定，只是一种自己的推测、推断。这时，就用 should do，主句也不用虚拟语气（will receice）。以下为《柯林斯词典》的解释和例句：
词典的解释是 You use should in conditional clauses when you are talking about things that might happen.
1. If you should be fired, your health and pension benefits will not be automatically cut off.
如果你被解雇，你的医疗和养老保险金不会自动中断。
2. Should you buy a home from Lovell, the company promises to buy it back at the same price after three years.
如果你从洛弗尔公司买房子，该公司承诺3年后以同样的价格再购回。（去掉if后，产生倒装。两个例句中，主句也都是陈述语气）
