shall什么意思 I shall know why -- when Time is over

I shall know why -- when Time is over  

I shall know why -- when Time is over --
And I have ceased to wonder why --
Christ will explain each separate anguish
In the fair schoolroom of the sky --
He will tell me what "Peter" promised --
And I -- for wonder at his woe --
I shall fet the drop of Anguish
That scalds me now -- that scalds me now!