“rolling on through the land slowly and surely, like a good man's life”
The narrator compares a steady river to a good life, using natural movement as an image for patient continuity and moral character.
Source details
John Halifax, Gentleman, represented by Project Gutenberg #2351. The phrase belongs to the first-person narrator Phineas Fletcher while describing the river; it is a literary simile inside the novel, not direct autobiography by Craik.