He's been speaking at the annual National Prayer Breakfast in Parliament which was attended by Prime Minister Theresa May, over 140 MPs and many church leaders.
Addressing the theme, 'What can Christianity offer our society in the 21st century?' Keller used the opportunity to issue a rallying call to British Christians.
He said: "Jesus' metaphor was that Christians could be salt as long as they're not the same as the meat - they're different.
"Christians won't benefit society if they're just like everyone else in society.
"We're not going to benefit society filled with self-actualisers unless we really are different and we do believe Jesus died for us and we live by self-sacrifice.
He also had a message for political leaders.
"Here's what British society can do to get the most benefit out of Christians," he said. "Don't demand that they become like everyone else. Modern society says we believe and respect difference but here's what you should do: tell Christians to be true to their ideals but then critique them on those ideals not on someone else's."
Those gathered at the event in Westminster took time to pray for politicians and for the UK and were also led in worship by Keith and Kristyn Getty.
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