In an organisation full of idealists and activists, I like to pride myself on my pragmatism. Colleagues often hear me say "You're right of course, but I think a lot of people would be more concerned about..." or, when we're pushed for time and need to get to a decision quickly, "Normal people just don't care about that".

But last weekend, even I had a burst of sanctimony.

I had just returned – via a delayed and quite frustrating lockdown and evacuation after we'd narrowly escaped a shooting in the grounds of a church – from the Central African Republic where I had met with women who had survived rape in the war that has been ravaging the country for the last couple of years. I was excited to see some great media coverage start to emerge, pointing people towards the Ending Sexual Violence in Conflict summit taking place this week in London.

But the momentum of the public debate stalled, when the ongoing saga of a spat between two UK Cabinet Ministers came to a head on Saturday evening with a compulsory apology and a staffer resignation.

It meant that the UK's Foreign Secretary, William Hague, interviewed on national TV on Sunday morning, had only a few seconds to talk about rape as a weapon of war before being quizzed about his colleagues instead.

My morning at church was punctuated with messages from journalists, apologising for not being able to report on the devastating effects of rape and sexual violence because they had to speculate about the implications of the politicians' argument on the future leadership of the Conservative Party.

By lunchtime, my anger levels (expressed silently, while still smiling at everyone in church, because I'm both British and trying to be a good Christian) were pretty high. 

But by Tuesday, when the summit opened, every national news bulletin and newspaper was covering it.

And it's all thanks to Angelina Jolie.

Give them their due, the journalists we'd spoken to months before had been broadly interested in the topic, and we and other NGOs had pulled out all the stops to make the stories work: we'd brought survivors of warzone rape to the UK, we'd hosted journalists in our projects serving survivors of sexual violence, we'd taken beautiful pictures showing the dignity and hope that is possible for survivors, we'd gathered compelling stories of the brutality and humiliation of rape and we'd commissioned research on how best to prevent it in future.

But the front pages were mostly of Angelina, and I didn't see a TV news item that didn't carry a shot of her.

She's worked extremely hard for more than two years, travelling to post-conflict states even while going through her own traumas, and brings a great deal of grace and wisdom to the debate.

Yesterday, I watched her thank rape survivors and faith leaders for leading churches and faith communities to speak out against sexual violence. She has poise, she makes people feel special and she's a truly beautiful person.

She has achieved a great deal in helping us bring together more than a hundred countries to agree that we will try to eradicate rape as a weapon of war.

But she knows, and we all know, that it's her celebrity status that is her main contribution.

Celebrities bring something to a cause that no-one else can bring: their reputation, profile and public recognition. If you're someone that people instantly recognise and warm to, it's much easier for you to get people interested in an important social justice cause. You don't have to spend time getting people to believe or trust you, because they probably already do.

In any story, people need to see something they recognise from their own world in order to relate to it, which makes pitching stories from other countries difficult. The people we meet in war zones or poor countries live very different lives to those of our supporters and the UK public.

We have to tell stories in a way that create empathy or that draw the viewer in somehow. When I met Lucienne in Central African Republic two weeks ago and found that she's the same age as I am, it was much easier for me to try to jump into her world and sympathise with her experience of being brutally raped at gunpoint by two men in front of her seven year old son even though I don't have a son and have never experienced anything like the violence she has known.

But that still isn't enough to get into every news bulletin. Viewers need to see someone they know, and bringing in a face they recognise from films or TV is hugely powerful in helping grab their attention.

It's not without its risks. Oxfam had a hard time when Scarlett Johanssen stepped down from being their ambassador in an effort to avoid conflict of interest with her commercial interests, which then dragged Oxfam into a debate about Israel and Palestine which I'm guessing they probably didn't want to have.

Most celebrities are aware of this and take their responsibilities seriously. In my experience of charity communications, there aren't many who jump on cause-related bandwagons for their own glory.

It's a lot of work for all of us, helping people who have reached the top of their game to espouse a cause and bring people towards finding a solution to some of the world's biggest problems. It takes time, money and a lot of energy and commitment from the celebrity, as well from the charity.

But, let's face it, if we're serious about bringing about change, we'll do whatever it takes to help people understand the complexities of social injustice and invite them to tackle it with us.

And celebrities are able to bring far more people to the party than we can on our own. As the unstinting efforts of people like Angelina Jolie have shown us, they give us much greater access to people's hearts and minds than we could have otherwise. The money, awareness and political action they generate is often greater than we could achieve without them.

It's their job to get people's attention. It's ours to use it well and wisely; to meet the needs of the world's poorest people and to change the structures that keep people poor. We can't do the former as well as they can, and they can't manage the latter without us.

Katie Harrison is Tearfund's head of communications.