In Coleridge's poem, "Frost at Midnight," several thoughts come to the speaker. The author (Coleridge) is sitting by the fire, in solitude that allow him to pursue "abtruser musings." While his thoughts may be hard for others to follow, he sees a connection between his own past and the future of his child—a son who sleeps in a cradle next to him, while the rest of the household has retired for the evening.
One thought that arises in the author's mind is how disturbingly quiet it is. The "silentlessness" rather than calming Coleridge, makes him agitated. He notes how unusual this lack of sound it, when the town is generally overrun by noise.
He sees the "stranger" (a flap of sooty film) on the fireplace's grate and recalls his years as a student away from home. The "stranger" was superstitiously supposed to announce the arrival of an absent friend. The author alone at school was still young enough to believe the superstition, and lonely enough to look for a friend or family member (such as his sister—who he dearly loved) to appear mystically at his school during these times of isolation.
How oft, at school, with most believing mind,
Presageful, have I gazed upon the bars...and as oft
With unclosed lids, already had I dreamt
Of my sweet birth-place, and the old church-tower...
As the author sits looking at his sleeping child, he hopes and anticipates (as does every parent, perhaps) that the future will hold so much more for his little boy than was offered Coleridge. While Coleridge (the Romantic poet, with a love for nature) only saw the sky and stars between buildings as he grew up, he hopes his son will wander over the face of the earth, "like a breeze," by lakes, along shorelines, around mountains, and beneath clouds. He expects God will grant him these things.
It occurs to Coleridge that with this kind of familiarity with nature, his son will perceive "all seasons [to] be sweet," wherever he goes and whatever the time of year.
Therefore all seasons shall be sweet to thee,
Whether the summer clothe the general earth
With greenness, or the redbreast sit and sing...
These are the main ideas that occur to the poet as he sits by the fire while their is "frost at midnight."