Lowell was approaching 50 years old, as he notes in the letter, and demands a "test of friendship" from Cranch: for his birthday, he wants him to pay a visit at the Lowell home, Elmwood. Though living in New York at the time, Cranch came through, and even wrote a birthday poem for Lowell. Perhaps as a response to Lowell's value of fame mentioned above, the poem concludes that "our love" makes "his fame."
The letter is sincere and warm, reflecting a friendship not generally recognized by history. Cranch, a minister, was also a poet and artist — and deserves the title of best sense of humor among the Transcendentalists. Lowell, for all his varied efforts, was also a humor poet, publishing his A Fable for Critics in 1848 at the age of 29.
As Lowell concludes his letter to Cranch:
My old clock in the entry has just given that hiccup with which tall fellows of their hands like him are wont to prelude the hours — and the hour is midnight. My fire and my pipe are both low. I must say good-night. I have had great difficulty in saying what I wished with this pen, which has served me I know not how long. But I have stood by it, and that should convince you (if you needed convincing, as I am sure you didn't) that I don't give up an old friend even when he has lost his point. But that is something you can never do for me, and I shall expect you on [my birthday]... You shall... have a warm welcome from Mrs. Lowell (who thinks you handsome — that way madness lies!).