The Joshua Camp is being run by the Sion Community for Evangelisation at St Bonaventure's Catholic high school.
People have come from 21 countries to take part in the event.
They were welcomed by the Bishop of Brentwood, Thomas McMahon, who highlighted two particular Olympic themes: carrying the torch and running the race.
He explained how the light was revered in ancient Greece and the torch became a symbol of "faith and hope in a darkened world".
A few weeks ago, the bishop welcomed the Olympic torch as it went past his cathedral in Brentwood.
He said he liked “to think that people also gathered to see and support those who were carrying the light”.
He challenged the youngsters in their faith, asking “Do we try each day to follow Christ our light? Are we light bearers to our world, to those around us, by our way of life, by the way that we witness to Christian values?”
Speaking on ‘running the race’, Bishop McMahon recalled how the ancient Games were nothing to do with medals made up of precious metals, or national flags and anthems but rather about “individual strength, skill, training, discipline and commitment”.
“It is sad when the emphasis today is solely on achievement," he said. "The earliest emphasis of the Games was on taking part rather than on achievement and success.”
Referring to New Testament writing, he impelled those present to see “life as a race, a marathon, with only one thing necessary for us Christians and that is not the winning so much as the keeping our eye on Jesus, remembering that our faith is not first and foremost built on teachings or doctrines or rules and regulations but around a person, the person of Jesus".
He challenged young people to go deeper in their faith and make sure Jesus was "real" rather than "notional" in their lives, and a "weekday friend" as opposed to a "Sunday acquaintance.
He concluded, “Run the race of life always with your eyes fixed on Jesus, knowing that this race isn’t for winners but rather for finishers.”