A dream within a dream

Take this kiss upon the brow
And in parting from you now
Thus much let me avow
You are not wrong who deem
That my days have been a dream
Yet if Hope has flown away
In a night or in a day
In a vision or in none
Is it therefore the less gone
All that we see or seem
Is but a dream within a dream.

I stand amid the roar
Of a surf-tormented shore
And I hold within my hand
Grains of golden sand
How few yet how they creep
Through my fingers to the deep
While I weep while I weep!
O God! can I not grasp
Them with a tighter clasp?
O God! can I not save
One from the pitiless wave?
Is all that we see or seem
But a dream within a dream?

study hard to understand this poem now. n its start to puzzled me so much.