But when the shadow dimmed and returned to the true, when he passed over and left the age, the golden face veiled its colour and no longer mirrored the light of the three thousand;

This is the Buddha's death, written so as not to say so. 晦影歸真 — the shadow dimmed and went back to the real. 遷移越世 — moved on and crossed out of the age. 金容, the golden face, is a standard epithet for the Buddha's body. 三千 is short for the three thousand great thousand-worlds — Buddhist cosmology's name for the whole universe. Four euphemisms in one line, and not one of them is the word died.

and the fair image was opened in outline, tracing on emptiness the thirty-two marks.

四八之相 — the four-eights marks, meaning thirty-two. A buddha's body is traditionally described as carrying thirty-two major marks, from the wheel on the sole of the foot to the crown-protuberance on the head. Its last character is read xiàng — an appearance, a mark, an image. Read xiāng it means mutually, which is how the bare chain takes it and how most readers meet it first. 空端 — beginning in emptiness. Once the man was gone, what was left was the picture: statues and paintings, marked out on nothing.

Thereupon the subtle words spread wide, rescuing the flocks of beings from the three evil paths;

微言 — subtle words, the standard phrase for a sage's teaching whose meaning is dense and short. 三途, the three paths — the hells, the realm of hungry ghosts, and the animal realm. The three worst places a being can be reborn into. The teaching's job is described here as extraction from them.

the bequeathed instruction was proclaimed afar, leading the host of the living to the ten stages.

十地 — the ten grounds, the ten stages a bodhisattva climbs on the way to buddhahood. The matched pair is exact: out of the three worst realms, up to the ten highest stages. 遺訓 — the teaching left behind. It picks up the death two lines earlier without naming it again.