"Evening in Paradise" is from the epic poem Paradise Lost written by John Milton.
In summary, the poem describes the approach of evening and the animals settling in for the night—except for the Nightingale that will sing all night long. Then stars appear in the sky and are then joined by the moon: they illuminate the darkness with light.
In the first two lines, the reader recognizes the imagery used in the form of personification.
...a figure of speech in which abstractions, animals, ideas, and inanimate objects are endowed with human form, character, traits, or sensibilities
"Evening" is referred to with the possessive pronoun "her," and the poet describes that she has "clad" (clothed) all things in the color of "Twilight gray." The idea of clothing something—and being clothed—is a human behavior, and the "Evening" is not human, but given human characteristics.
Now came still Evening on, and Twilight gray
Had in her sober Liverie all things clad... (1-2)
Lines five and six describe the singing of the "Nightingale." Imagery is used as the author describes her song as an "amorous descant," or a love song. (A "descant" is a "song or a melody.")
...all but the wakeful Nightingale;
She all night long her amorous descant sung... (5-6)
In line seven, "Silence" is personified. Silence is not a person, therefore it cannot experience emotions, such as (in this case) pleasure.
Silence was pleas'd... (7)
Note that in line seven, Milton refers to the "Firmament," which is "the vault of heaven; [the] sky." A metaphor is used once again: this time the two things being compared are the stars and "Saphirs" (sapphires). Both are shiny and bright (the characteristics they share), but one is a heavenly body of gases and the other is a gem.
Now glow'd the Firmament
With living Saphirs... (7-8)
In lines nine and ten, the author alludes to Hesperus. In Greek mythology, it was believed that Hesperus was the evening star or the planet Venus. In the poem, Hesperus ushers in the "starrie Host" (the stars)—he himself shining the brightest.
Hesperus that led
The starrie Host, rode brightest... (8-9)
Hesperus is the brightest of them all, but only until the moon appears. Once again, personification is used to describe "the Moon." The possessive pronoun is used ("her"), and she is described as uncovering ("unvail'd") her unequaled ("peerless") light—in doing so, the moon throws over the darkness a silver light ("her Silver Mantle threw"). The use of "mantle" is also an example of personification, in that a mantle (cloak or cape) is an article of clothing that people wear.
...till the Moon
Rising in clouded Majestie, at length
Apparent Queen unvail'd her peerless light,
And o're the dark her Silver Mantle threw. (9-12)
Milton's uses of imagery provide vivid descriptions that bring his subject matter alive.