21: But at my back I always hear: the word "but" emphasizes the passage to another stanza and especially from an imaginary scene to a real one.
Here a run-on-line is used, in order to speed the rhythm to give the idea of the passing of time.
The word "I" has got a central position to underline the "first person narrated".

22: Time's winged chariot hurrying near: the speaking voice makes reference to the time. He says that he hears at his back (as if it were a charge that he would bear on his back) the time's winged chariot. That means that he suffers for the passing of time and so death's arrival. The use of the winged chariot's metaphor is a topos imported by the Classicism.
The word "hurrying" (thanks also to the progressive tense)together with the use of the run-on-line help to emphasize life's transience.

23-24: And yonder all before us lie/Deserts of vast eternity: through a run-on-line, the speaking voice says that an eternal after death is waiting for them. But it is an incitement not to waste time and so not to be coy. "Vast" makes reference to soulfulness of love.
Both "yonder" and "vast" underline the distance from eternity, helped also by the alliteration of "s" and the use of long vowels.
In addition these lines don't rhyme, in order to make the reader pay more attention.

25: Thy beauty shall no more be found: after her death will be impossible to find such a beauty.
"Thy" is the archaic form of "your". No more has got a central position in order to add meaning to the situation's impossibility.It is an ironical statement,of course.

26: Nor, in thy marble vault, shall sound: the speaking voice says that something in her marble vault (so it is a precious vault) would not sound. The object is explained in the next line, by using a run-on-line.
Nor is linked to "no more" of the previous line, in order to emphasize impossibility again.
"Thy" is repeated because he only wants to refer to her.

27-28: My echoing song: then worms shall try/ That long preserved virginity: the object of the previous line is his echoing song. Of course, the song which he makes reference is declaration of love. After that he starts reproaching her as a consequence of her coyness. As a matter of fact he uses a colon and the word then, which marks a consequence of time.
In addition he uses a run-on-line (used to underline the speed) to explain that worms will taste her body and they will eat away at her purity and virginity, which she has preserved. These images help to create a feeling of disgust to her. The word "try" reminds to "thy" of the previous two lines and shall is repeated three time to highline his exhortation not to be coy in the future.

29: And your quaint honour turn to dust: by using a strong image, the speaking voice shows his reproach for her coyness. As a matter of fact he says that her honour is vain, because she will die (and so turn to dust). The meaning is emphasized by the alliteration of "t" and the word "quaint" which means old-world.

30: And into ashes all my lust: the line begins with the word "and", like the previous line. The anaphor produces a sense of link between these lines. The aim is to declare that with her death, he will lost all his lust as a consequence of it.

31: The grave's a fine and private place: his reproach carries on by making an unusual and ironical reference. As a matter of fact he refers to grave, which would surely be fine and private. But a grave could not be considered as something private and fine, but something frightful. The aim is always to convince her not to waste time.

32: But none, I think, do there embrace: the adversative pronoun underlines his objective and his conviction bases on the fact that when she dies, she will not hug nobody. Of course the statement "I think" (positioned at the center of the line to emphasize the first person narrated) is ironical, because he is sure of it.

33: Now therefore, while the youthful hue: "now" marks the fact that he starts to talk about the present and "therefore" highlines the consequence. "Youthful hue" makes reference to alive people's blush, in opposition of a dead person's paleness.
In this line the semantic field of time is used, to emphasize his main as throughout the poem

34:Sits on thy skin like morning dew: a run-on-line is used. The speaking voice wants to underline her youth by making a comparison with morning dew (symbol of freshness). Of course, it is ironical because his goal is to point out the passing of time and the fact that she should not waste time. The use of the verb "sit" emphasizes that it is a temporary situation and suddenly her hue can disappear (she can die) like dew in the afternoon.

35-36: And while thy willing soul transpires/ At every pore with instant fires: a periphrasis is used instead of saying: while you are living. The word "while" brings back to the first line of this stanza because the lines both are about the present. The soul is considered as something which transpire and burn with the passing of time. Therefore soul his mortal because suddenly it can stop burning.
Mortality is another great point to convince her

37: Now let us sport us while we may: that is a very important line, because the aim, which was implicit throughout the poem, becomes explicit. As a matter of fact the speaking voice incites her to do physical activity (that is the consummation of his sexual desire) as a consequence of all the argumentation he gave in order to convince her. That is underlined by the repetition of the word "us", which refers only to her and him .
"Now" ,instead, reminds the first line.

38: And now, like amorous birds of prey: "now" is repeated for three times in order to focus on the present. Besides repetition of "and" marks coordination of statements. A comparison with "birds of prey" and a run-on-line is used.

39: Rather at once our time devour: a deviation of common word's order is made. Therefore the reader pay more attention.
The simile with "birds of prey " is explained: as they, starving, dart to prey and they devour it, so the speaking voice and his beloved should devour time and put an end to his lust.
The comparison with birds reminds the previous topos ( winged chariot).

40: Than languish in his slow-chapt power: it is better to put to an end his lust, rather than become weaker and weaker with the passing of time and without satisfying his desire. Here a deviation of common word's order is made as well.

41-42: Let us roll all our strength and all/ Our sweetness up into one ball: he incites (as a matter of fact he uses the imperative form) her to put all their strength and sweetness together. The run-on-line and the alliteration of "all" add meaning to his desire of going on quickly not to waste time.

43: And tear our pleasures with rough strife: he uses violent images and words as "tear", "rough" and "strife" because his lust is so strong that it is ungovernable. It becomes even violent.

44: Through the iron gates of life: he incites her to reach pleasure and so even going beyond life. It is compared to iron gates, so something insuperable.

45-46: Thus, though we cannot make our sun/ Stand still, yet we will make him run: the poem ends by saying that since they cannot stop sun (which is a metaphor of life--> topos that links to Classicism) they could at least make life run by consuming his desire. A run-on-line is used and an alliteration of "u" as well to add meaning to it.