Rt Revd Richard Chartres was speaking to the more than 2,000 specially invited guests at St Paul's Cathedral who were celebating Premier Christian Radio's 20th anniversary.
He explained how, often the Christian voice in Britain seems faint and does not always reflect contemporary reality.
"The Christian voice in cyber space is too often absent, leaving far too much room for shrill and judgemental voices," he said.
"It's a cliché to say, but true, that the young are communicating in a different way and the allocation of Christian effort and resources reflects a communications culture of a previous age."
Broadcast live on Premier Christian Radio and via a webcast, the Bishop went on to say that Christianity is not in decline worldwide or in London but that it sometimes seemed to lack confidence.
"Change is indeed possible and Premier has led the way in imagining new ways, appropriate to our time, of singing the Lord's song in the spirit of the word made flesh."
The Bishop of London was joined at the event by the Riding Lights Theatre Company, worship leader Graham Kendrick and the All Souls Orchastra.
Listen to Bishop Richard's sermon here: