According to Malala Yousafzai in I Am Malala, what is more powerful than guns?

I thought that words and books and pens are more powerful than guns.

The quote comes from Diane Sawyer’s October 10, 2013 interview with Malala Yousafzai, a young girl from Pakistan’s Swat Valley whose human rights advocacy led to her attempted assassination by the Taliban.
In the interview, Yousafzai expands upon the remarks she made in her speech to the United Nations Youth Assembly on her sixteenth birthday, July 12, 2013, “Malala Day.”

Dear sisters and brothers, we realize the importance of light when we see darkness. We realize the importance of our voice when we are silenced. In the same way, when we were in Swat, the north of Pakistan, we realized the importance of pens and books when we saw the guns. The wise saying, "The pen is mightier than the sword." It is true. The extremists are afraid of books and pens. The power of education frightens them. They are afraid of women. The power of the voice of women frightens them. This is why they killed 14 innocent students in the recent attack in Quetta. And that is why they kill female teachers. That is why they are blasting schools every day because they were and they are afraid of change and equality that we will bring to our society. And I remember that there was a boy in our school who was asked by a journalist why are the Taliban against education? He answered very simply by pointing to his book, he said, "a Talib doesn't know what is written inside this book."

Yousafzai tells Sawyer that if she could confront a potential attacker, she would explain the importance of education, and she would tell him that she wants education even for his own daughter. Yousafzai believes that education is the most powerful weapon against terrorism, violence, poverty, and injustice. She continues to call upon world leaders to work toward free, compulsory education for boys and girls everywhere. It is the only way to challenge ignorance and ensure a peaceful future.