Я взяла эту книгу не только из-за сюжета; к тому же мне понравился спокойный язык автора.

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Breakdown of Я взяла эту книгу не только из-за сюжета; к тому же мне понравился спокойный язык автора.

• книга: the book
• спокойный: calm
• не только: not only

Questions & Answers about Я взяла эту книгу не только из-за сюжета; к тому же мне понравился спокойный язык автора.

Why is it взяла, not взял or брала?

Взяла is:

• past tense
• feminine singular
• from the perfective verb взять

So it tells you that the speaker is female and that she took/picked up/chose the book as a completed action.

Compare:

• я взяла = I took / I picked up
• я взял = the same, but said by a man
• я брала = I was taking / I used to take / I took (imperfective, less focused on a single completed result)

In this sentence, взяла fits because the speaker is talking about one specific act of choosing or taking the book.

What is the difference between взять and брать here?

These are an aspect pair:

• брать = imperfective
• взять = perfective

In this sentence, взяла from взять is used because the speaker means a single completed action: she picked up or chose the book.

Very roughly:

• Я брала эту книгу = I was taking this book / I used to take this book / I took this book (with less focus on completion, depending on context)
• Я взяла эту книгу = I took/picked up this book (completed action)

Russian often uses the perfective when talking about one finished event.

Why is it эту книгу?