Justine Greening is a senior cabinet minister, Secretary of State for Education, no less.

It is good that we try always to be polite when discussing our political leaders, setting a tone of sweet reasonableness in contrast to the snarling cynicism that characterises so much public discourse. But really: in her comments yesterday about same-sex marriage she showed such abysmal ignorance about religion that a snarl is the only appropriate response.

Greening told Sky News on Sunday: 'I think it is important that the church in a way keeps up and is part of a modern country.

'I wouldn't prescribe to them how they should deal with that,' she said, before proceeding to do so.

'I do think we are living in a country where people broadly recognise that attitudes are in different place now to where they were many, many years ago,' she said.

'We have allowed same-sex marriage, that's a massive step forward for the better.

'For me, I think people do want to see our major faiths keep up with modern attitudes in our country.'

Of course, the question of same-sex marriage is neither here nor there. Some Christians, and other people of faith, are for it; others are most definitely not. What betrays Greening's complete lack of any kind of understanding of religion is her belief that it should keep up with the times. Morality moves on, and the Church should move with it, she says.

Well, no, it doesn't work like that. There isn't a smooth progression from the darkness of superstition to the sunlit uplands of rationality, with the Guardian-reading Islington elite as the high priests of a new totalitarianism. The Church does not keep up with the times; it judges the times, and it's the times that are found wanting. If we are to be judged on whether we're willing to 'keep up with modern attitudes', so be it; most of us are happy to be out of step, because we're marching to the beat of a different drum. Of course people of faith are affected by wider currents of opinion and belief, but there is a root of faith from which all our convictions spring – and none of us care remotely about being 'part of a modern country', as if that were something that should trump those beliefs.

At one level, Greening's comments are just crass. But they are alarmingly self-revelatory, too. Her brief is education, and she is ultimately responsible for the formation of young people who are liberal-minded in the best sense: sympathetic, well-informed and able to understand the thought-worlds of those who are not like them while holding firmly to their own convictions. It's on her watch, too, that teachers and other professionals have to be on guard against young people being radicalised and turned into potential suicide bombers. Is it seriously conceivable that someone whose philosophical grounding is so shallow can discharge these responsibilities effectively?

Greening seems to conceive of faith as equivalent to fashion, and as easily changed: that dress or bag is so antique, darling – it's really time for a new one. 'Progress should mean that we are always changing the world to fit the vision,' said GK Chesterton. 'Instead, we are always changing the vision.' Yes – that's her line.

And he also said: 'A dead thing can go with the stream, but only a living thing can go against it.' The Church is alive. It doesn't care what the fashion is, it cares what's true. It will change its mind sometimes, but it will do so in its own time and on its own terms – and it won't care in the slightest what the world thinks.

Follow Mark Woods on Twitter @RevMarkWoods