The Church of England has gently modified God's first injunction in a new green guide for members, which suggests: let there be a little less light.
Clergy and congregations are being encouraged to cut the increasingly popular floodlighting of ancient churches to reduce parish carbon emissions.
The manual, Don't Stop at the Lights, suggests occasional community or sponsored evenings to make floodlighting more of a special occasion.
The guide also calls for a revival of the God's Acre tradition of churchyard management, using more of the land to provide havens for wildlife and plants. Vicars and churchwardens are asked to draw up modern versions of the medieval use of churchyards to grow yew - essential for longbows but banned from open pasture because its berries poisoned livestock.
The Archbishop of Canterbury, Dr Rowan Williams, said: "All Christians have an important role to play in developing their own environmental awareness and encouraging it in others. This will prove invaluable for those looking to find a deeper theological understanding of our Christian concern for creation."
The guide revives another medieval practice, still carried out in many parishes - the beating of the bounds. The origins of the annual procession round parish boundaries are obscure, but the new book suggests that the ritual has the potential to highlight green issues.
A spokesman for the church said that regular floodlighting would be acceptable if security was involved. The Bishop of London, the Right Reverend Dr Richard Chartres said: "This book offers us not just tips on energy saving but a reorientation.
"The intention is not to urge Christians to get measured for a hair shirt but to rediscover how good and joyful a thing it is to dwell together in unity with everything else that lives."