Yet heaven and earth enclose the dark and the bright and are easily known — and this is because they have images;

The document now explains itself, which is the mark of a good bureaucrat. Having stated the contrast, it gives the reason for it. 包乎 — enclose, contain. Heaven and earth are the container; yin and yang are what is inside. 以其有象也 — because they have images, that is, because you can see them.

the dark and the bright dwell within heaven and earth and are hard to fathom — and this is because they have no shape.

處乎 — to dwell within, to be situated in. Its first character is read chǔ here, the verb of residing. Read chù it is a noun, a place, which is how the bare chain takes it and how most readers meet it first. The pair is now complete and airtight: the container is visible, the contents are not, and that is the whole of why one is easy and the other impossible. Eight lines in, and the emperor has not mentioned religion once.

So we know that where the image is manifest and can be verified, even the foolish are not confused;

可證 — can be proved, can be verified. It is an evidentiary word, and it is doing evidentiary work: what you can check, you can be sure of. The argument is being built like a case, one clause at a time, each half answering the last.

where the shape is hidden and cannot be looked at, even in the wise there is bewilderment still.

在智猶迷 — even in the wise, still lost. Four characters, and they close the opening movement. The emperor has spent eight lines establishing one thing, and he has done it entirely with sky, seasons and logic: the visible can be known, and the invisible cannot, no matter who you are. That is the ground he needs. The next line is where the Buddha comes in.