It made the slovenly wilderness Surround that hill. (3-4)
These lines give us our first glimpse of the transformative power of the jar. It doesn't mess around, but starts taking names and giving orders as soon as it touches down on that Tennessee hill, rearranging the wilderness as it sees fits.
The wilderness rose up to it, And sprawled around, no longer wild. (5-6)
Here, we see that the wilderness isn't even really putting up a fight. It's going to the hill without struggle and losing its wildness. This makes us think about the transformative effect of perspective—the wilderness probably isn't literally becoming less wild, but it is in the eye of the speaker.
And tall and of a port in air. (8)
Ports are places of transformation. They are where sailors get their land-legs, and where people go from one country to another, looking for new life. This jar is a port in air, not water. Through it, the view of the wilderness (untamed and wild, or subjected to the jar's dominion) can go in and out on the breeze, changing as it passes through man-made glass.
The jar was gray and bare. (10)
Unlike the wilderness, the jar doesn't transform at all in this poem. It's gray, bare, and, we're betting, round, just like it was at the beginning of the poem.
It did not give of bird or bush (11)
Here is another line to show how static, or unchanging, the jar is. Unlike the wilderness, which—under the rule of the jar or not—can procreate and grow, the jar is stuck in its original boring shape.