There they were, dignified, invisible,The ghosts of the past are invisible. Previously I have been emphasising the non-existence of the past, or that it is no more than a 'speculation', but in this section Eliot does make room in the present for the ghostly persistence of the past, although it can't be seen or heard.
Moving without pressure, over the dead leaves,
In the autumn heat, through the vibrant air,
And the bird called, in response toThe leaves, the shrubbery, represent the past. The bird, which is the present, responds to the silent music of the past. The roses, which are present, are different because they were looked at in the past. By ghosts.
The unheard music hidden in the shrubbery,
And the unseen eyebeam crossed, for the roses
Had the look of flowers that are looked at.
There they were as our guests, accepted and accepting.Dryness, leaves, formality, ceremony, this is one way for humans to relate to the past - with a respect that inhibits and enfolds us. Ceremonial pattern links the past and the future.
So we moved, and they, in a formal pattern,
Along the empty alley, into the box circle,
To look down into the drained pool.
'Box circle' means a circular hedge at the centre of a formal knot-garden. Box is a shrub which is quite dull, but very dense and suitable for topiary. Another reference to leaves. But 'box circle' also makes me think of the theatre, where the words are rehearsed and pre-ordained, and also of Vitruvian Man, which represents the ideal formal or platonic version of the human body.
So, I take this section to be about a way of reconciling ourselves to the passage of time, which is through formal stately calmness and ceremony. It is low on excitement, but it allows us to spend some time in the rose garden, before it all goes wrong.
When Eliot depicts his transient happiest times he describes bright warm weather alongside organic sterility. Natural fecundity and uncontrolled growth disturb him. Bright sun in the middle of winter, or as here autumn heat on dead cut leaves. These are soothing images to him.