Answer:
I would contend that the lines that have a more serious tone are these: I am offering this poem to you, since I have nothing else to give, and when the world outside no longer cares if you live or die; remember, I love you.
Step-by-step explanation:
The speaker in this poem starts and finishes his declaration of love with references to his lack of material wealth. These parts of the poem feature a more serious tone. He then asks his beloved one to keep the poem, and his love, like a humble, but necessary, object. It is here, and throughout the next two stanzas, when he employs a visually descriptive and figurative language: a warm coat, a pair of thick socks. He then compares the poem and his love to a pot full of yellow corn and a scarf for your head, two equally simple, but very comforting, things. Lastly, he compares his love to a compass and to a warm and safe place in the middle of the wilderness (a reference to senectitude), finishing with a praise to love.