Rupert Brooke's poem Peace is a sonnet. It contains fourteen lines (eight in the first stanza and six in the second). The rhyme scheme of the poems is as follows:
a,b,a,b,c,d,c,d (stanza one)
e,f,g,e,f,g (second stanza)
This specific rhyme scheme makes it a Petrarchan sonnet.
Specific poetic devices found within the poem are alliteration, assonance, and personification.
Alliteration is the repetition of a consonant sound within a line of poetry. Alliteration can be found in the first line of the poetry (given the repetition of the "h" sound).
Now, God be thanked Who has matched us1 with His hour.
Assonance is similar to alliteration, but a vowel sound is repeated. Assonance can be found in the third line of the poem with the repetition of the "a" sound.
With hand made sure, clear eye, and sharpened power.
Personification is the giving of human characteristics to non-human/non-living things. Examples of personification can be found in lines twelve and fourteen.
Nothing to shake the laughing heart's long peace there.
In line twelve, the heart is given the ability to laugh (a human characteristic).
And the worst friend and enemy is but Death.
In line fourteen, Death is personified in two ways. First it is capitalized (making it into a proper noun). Second, it is given the ability to be a friend and enemy.