What did Robert Frost mean by the quote We dance round in a ring and suppose But the Secret sits in the middle and knows?

We dance around/spin our wheels/go in circles 'supposing', without really knowing what something/someone is about, and ultimately continue going in circles. But if we actually stopped/left the circle/ got off the merry-go-round and took the time to look inward (the secret lies within [the circle]) and reflect, we would have a better chance of figuring it (the secret) out. The secret lies within (the circle). It's just sitting there...knowing... and waiting to be discovered. Kind of the same, but opposite from looking within, is the old adage of 'seeing the forest through the trees', only in this way you are removing yourself from being too close to a situation in order to finally figure something out. Another one I like is the idea of simply 'letting go'... Many times it takes surrendering and letting go so that the 'something can unfold'... then you can finally figure it out.

Additionally:Be careful not to confuse the poet with the message of the poem. Often the poet is little more than the conduit, the vehicle by which the poem comes into existence. Sometimes the poem is the voice of the poet, but not always, and in the case of Frost, it could go either way. Frost writes on a much deeper level, although he is very often inspired by very real, tangible things. Look first at the simple things in Frost's work before you go deeper. Sometimes there is an elephant in the room, sometimes right there in the middle of the ring.

Sorry for the mixed metaphors; I just couldn't resist.

"Dancing" refers to thinking and figuring out. The secret, or mystery, can't be

figured out or approached by thinking. Who are you between thoughts?