We are told that we are at war. It certainly feels like it, with much of the economy being either shut down or mothballed, citizens having wartime restrictions placed upon them and the situation changing from day to day.

C S Lewis faced a similar although graver providence when in the autumn of 1939 the Second World War broke out, and he found himself preaching a sermon in the Church of St Mary the Virgin in Oxford, to the students of the university. It is still a stunning sermon from which we have much to learn and to apply in our own situation.

He argues that we should have "an intimate knowledge of the past" – not because the past is 'magical' but because we cannot study the future and yet we need something with which to compare our current circumstances.

"A man who has lived in many places is not likely to be deceived by the local errors of his native village: the scholar has lived in many times and is therefore in some degree immune from the great cataract of nonsense that pours from the press and the microphone of his own age," he writes.

One can only guess at what Lewis would have said about the 24/7 outpouring on social media and the internet! There is much we can learn from the past. The trouble is that our news is filled with predictions about the future – about which we cannot know (but fear) – rather than what we do know.

Lewis argues that the war does not create a new situation. 

"It simply aggravates the present human condition so that we can no longer ignore it," he argues. 

We tend to think this situation is new. And in one sense it is – because we personally have not experienced this before. But our experience is not the determiner of reality. Lewis reminds us that human life has always been lived on the edge of a precipice and that "human culture has always had to exist under the shadow of something infinitely more important than itself".

In his sermon Lewis warns us of three dangers in terms of our attitudes when we are faced with this kind of war.

The first enemy is excitement: that feeling when we are so caught up in the moment of the current crisis that we can think of nothing else. When the bushfires here in Australia were at their height, every day I checked my bushfire app to see how many there were and what was happening. Now I have a coronavirus app – so I can check the spread of the virus all over the world. It is all too easy to get caught up in something so that nothing else gets into your heart and mind.

The second enemy is frustration. For Lewis, this is the feeling that we will not have time to finish anything so why bother? What's the point of study, or getting married, or starting a new project when we live in a world in such a state of crisis? The Christian has an answer to that. We know that 'under the sun' everything is meaningless. But we know that there is more to life than that which is just 'under the sun'. We look to the eternal and so we can appreciate the present and work for the future.

The third enemy is fear. I see it in the faces of the people keeping their distance from me on the train. I hear it in the panicked voices on radio call shows. I feel it in my own heart and mind. Lewis points out that war threatens us with death and pain, and that no Christian should be stoically indifferent to that. But then he points out the rationally obvious, but something that is emotionally distant for most of us:

"What does war do to death? It certainly does not make it more frequent; 100 per cent of us die, and the percentage cannot be increased. It puts several deaths earlier; but I hardly suppose that that is what we fear.....Yet war does do something to death. It forces us to remember it. The only reason why the cancer at sixty or the paralysis at seventy-five do not bother us is that we forget them. War makes death real to us; and that would have been regarded as one of its blessings by most of the great Christians of the past. They thought it good for us to be always aware of our mortality. I am inclined to think they were wise."

We are at war. The Church is always in the midst of a war – against sin, suffering and Satan. This particular battle is both a test of our faith and an opportunity for us to live and proclaim it. O Church arise and put your armour on....

David Robertson is director of Third Space in Sydney and blogs at www.theweeflea.com