The expense of spirit in a waste of shame
Is lust in action; and till action, lust
Is perjured, murderous, bloody, full of blame,
Savage, extreme, rude, cruel, not to trust,

Enjoy'd no sooner but despised straight,
Past reason hunted, and no sooner had
Past reason hated, as a swallow'd bait
On purpose laid to make the taker mad;

Mad in pursuit and in possession so;
Had, having, and in quest to have, extreme;
A bliss in proof, and proved, a very woe;
Before, a joy proposed; behind, a dream.

Sonnet 129 is an Shakespeare sonnet and has the typical structure of three four-line stanzas and a final couplet composed in iambic pentameter.

Now I am going to analyze sonnet 129, Th' Expense of Spirit:

Considering the first stanza you have some adjective that describes the "expense of spirit" as the act of lust. In fact "lust" is a feeling of strong sexual desire for someone and Shakespeare uses a long series of adjectives that creates a negative climax. So in the first stanza you can find the definition of lust and the negative effect that it involves before the consummation.

The second stanza describes what happens immediately after the consummation. No sooner is lust "enjoyed" than it is "despised." In a mad way the act is hunted (animal area) and "no sooner had" it is in the same way, madly, hated and it becomes shameful.  The lust has also the function to "make the taker mad".

In the third quatrain, then, the speaker says that lust is mad in all three of its forms: in pursuit and possession, it is mad, and in memory with "had, having", and "in quest to have" it is "extreme." At the beginning that experience is like "a bliss in proof", but as soon as it is finished ("proved") and it becomes "a very woe". So it is before "a joy proposed," but  the pleasure behind is more like "a dream."

In the couplet, the speaker says that the whole world knows these things well; but nevertheless, none knows how to hide lust in order to keep away from shame: "To shun the heaven that leads men to this hell."