The poem says:

Chapters open the way an opera opens with an overture: a short regulated poem (七律) that states the moral before a single thing has happened. Read it as the chapter telling you in advance what it thinks the story means.

A hundred years of light and shade run on like flowing water; a lifetime's labors and affairs are but foam upon the tide.

Chinese says time by saying 光陰, guāng yīn — literally "light and shade," the sun moving across a wall. It is still the everyday word. Against that the poet sets 浮漚, fú ōu, "floating foam," a Buddhist figure for whatever swells on the surface of things and then is not there. A whole career, the line says, has the life expectancy of a bubble.

Yesterday the cheek still bore the peach-bloom's colour; today about the temples drift the flakes of snow.

One line, two faces of the same man. 昨朝, zuó zhāo, is "yesterday," with 朝 in its morning sense (zhāo) rather than its court sense; it pairs off against 今日, "today." Peach-blossom in the cheek, then snow at the temples — youth to old age in the space of a couplet.

Only when the white-ants' battle-lines lie broken is the whole seen as a dream; while the cuckoo cries in earnest, turn back betimes.

Two allusions a Ming reader would have caught at once. 白蟻陣, the white-ants' battle-lines, points to 南柯一夢, "the dream of the southern branch," from Lǐ Gōngzuǒ's Tang tale 《南柯太守傳》: a man dozes under a locust tree, lives out a glittering official career in a kingdom that turns out to be an ant colony in the roots, and wakes. It is the standard Chinese shorthand for a career that looked real and was not. Then the cuckoo, 子規, zǐ guī, also called 杜鵑: Chinese hears its call as 「不如歸去」, "better to go home," which is why the bird turns up wherever a poem wants a traveller to turn back.

From of old, hidden merit can lengthen a man's span; do good and beg no pity, and Heaven of itself provides.

The turn from renunciation to action. 陰騭, yīn zhì, is merit banked quietly where nobody sees it — the same idea as 陰德, and the phrase goes back to the 《尚書·洪範》: 「惟天陰騭下民」, Heaven settles the people unseen. 天自周 means Heaven completes the account of its own accord, with no invoice from you. This is the doctrine of 善果, good fruit from good deeds, and the chapter is about to act it out at full length: an emperor is going to be given twenty extra years, and the reason will be a favour done years earlier without expectation of return.