Theory:

What is Repetition?
Repetition is an act of repeating a word or phrase. It is commonly used to stress a point or to make a statement. It also helps in enhancing the general tone and style of the literary text. Hence, when used, repetition modifies both the form and the meaning of the text.
Definition:
According to J. A. Cuddon, repetition is “an essential unifying element in nearly all poetry and much prose. It may consist of sounds, particular syllables and words, phrases, stanzas, metrical patterns, ideas, allusions and shapes. Thus refrain, assonance, rhyme, internal rhyme, alliteration and onomatopoeia are frequent in repetition.”
The following is a famous speech from Shakespeare's Julius Caesar, spoken by Mark Antony. Shakespeare has used the rhetorical device known as repetition to deliver the message. The lines "Brutus says he was ambitious" and "Brutus is an honourable man" are examples of repetition, and one can easily see how the repeated lines had a positive impact and effect on the outcome of the speech.
Example:
Friends, Romans, countrymen, lend me your ears;
I come to bury Caesar, not to praise him.
The evil that men do lives after them;
The good is oft interred with their bones;
So let it be with Caesar. The noble Brutus
Hath told you Caesar was ambitious:

If it were so, it was a grievous fault,
And grievously hath Caesar answer’d it.
Here, under leave of Brutus and the rest–
For Brutus is an honourable man;
So are they all, all honourable men–
Come I to speak in Caesar’s funeral.
He was my friend, faithful and just to me:
But Brutus says he was ambitious;
And Brutus is an honourable man.

He hath brought many captives home to Rome
Whose ransoms did the general coffers fill:
Did this in Caesar seem ambitious?
When that the poor have cried, Caesar hath wept:
Ambition should be made of sterner stuff:
Yet Brutus says he was ambitious;
And Brutus is an honourable man.

You all did see that on the Lupercal
I thrice presented him a kingly crown,
Which he did thrice refuse: was this ambition?
Yet Brutus says he was ambitious;
And, sure, he is an honourable man.

I speak not to disprove what Brutus spoke,
But here I am to speak what I do know.
You all did love him once, not without cause:
What cause withholds you then, to mourn for him?

O judgment! thou art fled to brutish beasts,
And men have lost their reason. Bear with me;
My heart is in the coffin there with Caesar,
And I must pause till it come back to me.
The above speech has got various kinds of repetition in it, such as refrain, polyptoton, and anadiplosis. Apart from emphasising the meaning, the technique of repetition had also created an impact in the style by giving it rhythm.
 
Hence, repetition can affect both the form of the text as well as its meaning.
Why is the repetition important?
Repetition is important because it helps the speaker or author emphasise the important points. It also helps the audience or readers to understand the meaning of the poem or speech very easily.
Repetition used in the poem "Macavity: The Mystery Cat":
Macavity’s a Mystery Cat: he’s called the Hidden Paw —
For he’s the master criminal who can defy the Law.
He’s the bafflement of Scotland Yard, the Flying Squad’s despair:
For when they reach the scene of crime Macavity’s not there!
 
Macavity, Macavity, there’s no one like Macavity,
He’s broken every human law, he breaks the law of gravity.
His powers of levitation would make a fakir stare,
And when you reach the scene of crime Macavity’s not there!
You may seek him in the basement, you may look up in the air —
But I tell you once and once again, Macavity’s not there!
 
Macavity’s a ginger cat, he’s very tall and thin;
You would know him if you saw him, for his eyes are sunken in.
His brow is deeply lined with thought, his head is highly domed;
His coat is dusty from neglect, his whiskers are uncombed.
He sways his head from side to side, with movements like a snake;
And when you think he’s half asleep, he’s always wide awake.
 
Macavity, Macavity, there’s no one like Macavity,
For he’s a fiend in feline shape, a monster of depravity.
You may meet him in a by-street, you may see him in the square —
But when a crime’s discovered, then Macavity’s not there!
 
Important!
The word "Macavity" is often repeated throughout the poem. On the other hand, as you could see, there are several other words or lines that are highlighted, denoting the different kinds of repetition being used. Let us look at each one of them in the following materials.
    Reference:
  • Cuddon, J.A. A Dictionary of Literary Terms and Literary Theory. West Sussex, Wiley-Blackwell Publication, 2013.
  • https://www.poetryfoundation.org/poems/56968/speech-friends-romans-countrymen-lend-me-your-ears
  • National Council of Educational Research and Training (2007). Honeycomb. The Shed: Frank Flynn (pp. 48 -49). Published at the Publication Division by the Secretary, National Council of Educational Research and Training, Sri Aurobindo Marg, New Delhi.
  • National Council of Educational Research and Training (2008). Honeydew. Macavity: The Mystery Cat - T. S. Eliot (pp. 50-51). Published at the Publication Division by the Secretary, National Council of Educational Research and Training, Sri Aurobindo Marg, New Delhi.