Abbot Christopher Jamison, star of the BBC television series The Monastery and a former head master of a leading independent school, warned that rampant consumer culture is taking over people's moral purpose as their material needs are now all met.
He urged people to enjoy the month of Advent rather than celebrating Christmas early.
The Abbot of Worth School, a Benedictine boarding school in West Sussex where he was previously headmaster, also blamed the current economic crisis on a "lethal combination" of lack of ethics and an excess of regulation in the world of finance.
In a lecture at London's St Alban the Martyr church to coincide with a new "Reclaim Christmas" campaign by the Christian group Operation Noah, Abbot Jamison will say: "Our Western culture is saturated with goods.
"The economically stable individuals and households who make up the majority of our population have more stuff than they actually need.
"While they might be persuaded to buy some more or different versions of what they already have, business recognises this material saturation and so the present thrust of consumerism is towards selling culture as well as things.
"Having saturated the world of our material needs, consumerism is now taking over our need for cultural goods such as music, entertainment and even moral purpose."
He cited the example of a section of Nike's website, called 'Addicts Gallery', in which runners talk about sport as their "higher purpose".
"Even our souls are now consumerised and marketing is taking over not only our material imagination but also our spiritual imagination," the Abbot said.
"So Nike and the other great corporations now inhabit our imagination, the place where greed is generated. Once planted there they can make us endlessly greedy. And that is exactly what they are doing."
He denounced the "shopping frenzy" of the run-up to Christmas, followed by one day of peace and goodwill "then looking forward to the sales", and encouraged people to celebrate "temperance" during Advent.
The Abbot also told how he was once involved in a project to promote ethical training among bankers that the Financial Services Authority, the UK's City watchdog, commissioned but later ditched.
"The ethical project was over, the window of opportunity was closed and five years later the consequences are clear. While there are many proximate causes of the current financial crisis, the ultimate cause is ethical," he said.
"We can now see that the financial services industry was both over-regulated and unethical, a lethal combination, like a school with strict teachers where amazingly the pupils still get away with murder."
He also called for a new "ethics project", similar to the development of human rights in recent decades, to safeguard the environment.
