Keller was asked by the PCA to start Redeemer in 1989 despite his relative lack of experience and after two others had turned down the position. The church grew from 50 people to a total attendance of over 5,000 people each Sunday as of 2008, leading many to call him "the most successful Christian Evangelist in the city." In 2004 Christianity Today praised Redeemer as "one of Manhattan's most vital congregations", and, according to a 2006 survey of 2,000 American church leaders, is the 16th most influential church in America. His target audience consists mainly of young urban professionals, whom he believes exhibit disproportionate influence over the culture and its ideas. In his preaching, "he hardly shrinks from difficult Christian truths, [but] he sounds different from many of the shrill evangelical voices in the public sphere." He shuns the label "evangelical" because of its political and fundamentalist connotation, preferring to call himself orthodox because "he believes in the importance of personal conversion or being 'born again,' and the full authority of the Bible."
Keller has been described as a "C.S. Lewis for the 21st Century", although he has disavowed comparisons to his hero. He frequently draws on secular or academic sources like The New York Times, and media coverage has treated him as an anomaly: a pastor who appeals to Manhattan yuppies and intellectuals.
Some of his major and best-known teachings include idolatry as applying to modern problems like overwork or partisanship, the doctrine of the gospel as contrary to traditional religion (including institutionalized Christian churches), the importance of cities as a cultural force, and a moderate political stance. Keller mentors and chairs a network of center-city churches that represents these values worldwide.
Keller has been described by Mark DeVine as a "doctrine-friendly emerging pastor". A signatory of the Manhattan Declaration, he is opposed to same-sex marriage and abortion. Keller believes that "Marriage provides the personal growth that comes through cross-gender relationships." and was quoted as saying "Homosexuality, prostitution, sex outside of marriage, and adultery all fall outside of what God says he has designed sex for." He considers his opposition to abortion as a matter of human rights, but is not opposed to contraception.
^Hart, D. G. (2013). "Looking for Communion in all the Wrong Places: Tim Keller and Presbyterian Ecclesiology". Engaging with Keller: Thinking Through the Theology of an Influential Evangelical. p. 217.
^DeVine, Mark (2009), "The Emerging Church: One Movement, Two Streams", in Henard, William; Greenway, Adam, Evangelicals Engaging Emergent: A Discussion of the Emergent Church Movement, Nashville, TN: B&H, pp. 17–18.