Writing in The Daily Telegraph, he said the reforms were not just about “making the numbers add up”, but were intended to bring “new hope” to people who had previously been written off by the system.
“Our long-term economic plan for Britain is not just about doing what we can afford, it is also about doing what is right,” he wrote.
“Nowhere is that more true than in welfare. For me the moral case for welfare reform is every bit as important as making the numbers add up.”
Mr Cameron said that while the church was entitled to speak out on political issues, he did not accept the archbishop’s claim that the system was becoming increasingly “punitive” and that the situation in which many people now found themselves was “a disgrace”.
“Of course, we are in the middle of a long and difficult journey turning our country around,” Mr Cameron said.
“That means difficult decisions to get our deficit down, making sure that the debts of this generation are not our children’s to inherit.
“But our welfare reforms go beyond that alone – they are about giving new purpose, new opportunity, new hope – and yes, new responsibility to people who had previously been written off with no chance.