To what is the nautical imagery applied in 2.10? what is this poem about?

Horace achieves closure in his argument by repeating the nautical imagery from the beginning of the poem. The poet’s advice to pull in swollen sails brings to mind the warning at the opening of the poem not to sail out too far or stay too close to shore Horace nevertheless has subtly shifted the meaning in the two images. Ode 2.10 begins with advice to stay the middle course, while it ends with the more positive encouragement to remain strong whatever difficulties fate brings.Check out this link for more,

http://ufdcimages.uflib.ufl.edu/UF/E0/01/43/27/00001/burt_k.pdf