The poem
Awake, awake my little Boy! Thou wast thy Mother's only joy: Why dost thou weep in thy gentle sleep? Awake! thy Father does thee keep.
"O, what land is the Land of Dreams? What are its mountains, and what are its streams? O Father, I saw my Mother there, Among the lillies by waters fair.
Among the lambs clothed in white She walked with her Thomas in sweet delight. I wept for joy, like a dove I mourn— O when shall I return again?"
Dear child, I also by pleasant streams Have wandered all night in the Land of Dreams; But though calm and warm the waters wide, I could not get to the other side.
"Father, O Father, what do we here, In this land of unbelief and fear? The Land of Dreams is better far Above the light of the Morning Star."

This is a brilliant poem of loss and grievances. in my opinion, The widower and his child are trying to hold together after the loss of a dear mother and wife.
And dreams, in their development, have breath And tears, and tortures, and the touch of joy; They leave a weight upon our waking thoughts.... They make us what we were not - what they will, And shake us with the vision that's gone by … (Byron, 'The Dream', 5- 7, 15- 16) (from the Romantic Audience Project website)... Dreams bring calm and torture to the father and his child. They both have been to the dream land,…
Read the whole commentAnd dreams, in their development, have breath
And tears, and tortures, and the touch of joy;
They leave a weight upon our waking thoughts....
They make us what we were not - what they will,
And shake us with the vision that's gone by …
(Byron, 'The Dream', 5- 7, 15- 16) (from the Romantic Audience Project website)...
Dreams bring calm and torture to the father and his child. They both have been to the dream land, but reality brings them back. The son wonders why they live in a land of unbelief and fear, and the father "could not get to the other side." The son sees more than the father and experiences tears of joy; the father wanders and perhaps has too much "experience" to allow him to fully enter the land of dreams. The son has to question the father about the land, and interestingly enough, also realizes that it is "above the light of the Morning Star."