The first line of the sonnet, as the title, the speaking voice gives a statement. Shakespeare states the lust is "Th' expense of spirit in a waste of shame", this phrase indicates the moment when a men consumes energy and sperm for "enjoyed lust" with what the poet refers to the orgasm.
The first quatrain has the function to describes lust, and the key position focuses the reader's attention. Lust is "perjured, murd'rous, bloody, full of blame, Savage, extreme, rude, cruel, not to trust", where there are the alliteration of the harsh sound of "ur" in "perjured, murd'rous". This syntactic choice underlines the strength of lust; indeed the lust is a strong passion, it resides in human beings and it controls their actions. "Savage" refers to animal instinct, indeed also humans are animals. "Rude, cruel" are the behaviors of people that try to have the joy of lust with violence.
Shakespeare describes lust as "perjured" and "not to trust", to say this desire is often false like woman who pretends orgasm. In the second quatrain indeed, the poet focuses his description on the "swallowed bait" and "taker", that is usually woman.
In the second line of the second quatrain the word "hunted" is followed by a comma, so the speaking voice wants the reader gives attention to this word and he or she takes a pause to reflect on it. In English language haunting means the spirit infestation of the body so the lust haunts the human body and it takes the control. The word spirit is also in the first line.
People try to have this joy with all the ways and they became "mad"; "mad" when they had, have and having it. The madness takes person to do something without thinking, so mind doesn't control body's actions but on the contrary it is subjected to this.
In the third quatrain the distance between "a bliss" and "very woe" underlines the difference between the joy felt at the beginning and the sorrow felt at the end, and the sounds choice of "o" in "proof and proved" highlights this remoteness. In addition in the next line there are the word "Before" and "behind" and the couplet "heaven" and "hell", so the poet puts these word in correspondent position in the poem to underline the similarity and the difference of their meanings.
Shakespeare expresses medieval concepts: in middle ages the sexual act and all material desires were considered sins and who surrendered to the passions he went to the hell. In the couplet the poet says the human beings know the joy provoked by sexual act, that seems heaven but when the joy finished they doesn't know to avoid hell.