请问：关于此句英语的句型

题目

请问：关于此句英语的句型
句子如下：
If we glimpse the unutterable ,it is unwise to try to utter it ,nor should we seek to invest with significance that which we cannot grasp.参考译文：如果我们瞥见只可意会不可言传的事物,企图把它说出来,那是不明智的；对于我们不理解的事物,也不应该去赋于它某种意义.
此句话中,to invest with significance that which we cannot grasp significance 是个名词,其后的that 和which 在句中作什么成份?哪一个是定语从句的先行词?
significance 后面是定语从句，应该其后只要用一个先行词that 或which ,为什么that 和which 一起并列出现？他们在定语从句中分别作什么成份？

答案

调整到正常的语序应该是invest significance with that which we cannot grasp.其中which是定语,that是代词,用来指代我们不理解的事物.
补充:invest significance with sth 是指赋予某事某种意义 that which we cannot grasp 中that是先行词,which引导的定语从句修饰that.