分析一下句子结构,主要是but 后面的.

我们的血肉会消失,我们的双手会枯萎,然而它们所创造的真善美将永存.
that which=the thing that
也等于 引导词 what
如,I understand that which you said is correct.= I understand the thing that you said is correct.= I understand what you said is correct.
that which they create in beauty and goodness and truth lives on for all time to come.中,that which they create in beauty and goodness and truth是主语从句,lives on谓语,for all time to come状语,修饰lives on

But是连词，意思是“但是”，难理解的主要是后面，which引起的是定语从句，修饰that（that是先行词），所以but后面句子的主干是that lives on for all time to come。整句话的意思是：我们的血肉之躯将会消亡，我们的双手将会萎缩，但是他们用美、善、真创造的一切将永远存在。...

我们的肉体可能会消亡，我们的双手会干枯，但我们在真善美中所创造的，将一直存在下去。
That是主语，which they create in beauty and goodness and truth修饰主语；谓语是lives on，表示继续存在。