The answer is “Herbert uses Narcissus' rejection of Echo to
illustrate a holy man's rejection of mortal love for the eternal love of God”
<span>Herbert uses his poems to describe the relationship of humans
and God. He believed that by using the story of Echo and Narcissus, he wanted
the readers to see the relationship of God and His people. He had represented
the people as Narcissus while he had used Echo to represent God.</span>
The best way according to him is to make a good fence. The poem's final lines says that good fences make good neighbors. That can mean that if you stick your nose in your yard you will have good neighbors. Of course, this is all figuratively and refers to much greater things in life.
Using the formula:

Which is, 3.14 x 2^2 (radius is half of diameter)
Which equals 12.56.