"Our calling is to be a people who seek and serve Christ together, to be churches alive in the promise of God's world-transforming love," the Rev Dr Samuel Kobia says.
The message, released in the season of Epiphany, is for the period until 2013 (reflecting plans made since the WCC's 9th assembly last year in Brazil).
The message says "ecumenical Christianity for the 21st century" stands on that common experience of Christ and on "a common understanding of a world shared with all of humankind".
Dr Kobia said churches must respond to many global challenges, including the areas of human rights, care for the earth and its climate, and overcoming violence.
"Churches in many places will have to find new ways of witness in the world. We will have to pray for unity and seek it, perhaps especially in working for justice and reconciliation, and in developing inter-religious partnerships for joint action on difficult issues," Kobia suggests.
He outlines six new programmes for the WCC secretariat "as the global instrument of this fellowship".
"While much in our world pulls us apart, the opportunities to find strength in unity today may be greater than ever before," the general secretary says.
"Life is given to us not for domination or self-centredness, but for sharing, thankfulness, conviviality and joy," the Epiphany message concludes. "We are to find our place in the world together, as believers in God and as churches for the world."
