Are you on twitter? If that last sentence sounds like a random set of words with no obvious relationship to one another then it probably puts you in a, let's say, older age bracket. Twitter is, and I quote, "a social networking and microblogging service that allows you answer the question, "What are you doing?" by sending short text messages 140 characters in length, called "tweets", to your friends, or "followers."

Now already, I have probably lost some of you – social networking, microblogging – what's that? Well, it's all about sending out brief and instant messages over the internet. I don't twitter myself (can't keep me to 140 characters), but I am on Facebook, I do send emails and recently, grudgingly, have been known to send texts. Brief messages sent out into the ether, messages in a bottle, saying, "I am here. Talk to me". I wonder if some people couldn't use Facebook, Twitter, MSN, they might feel as though they hardly exist at all, but we are communicators by nature and in a modern, fast moving and technologically advanced culture we like our communications to be instant.

It was not, of course, always thus. If you wanted to send a brief message in previous years you had two main means of so doing. You could send a telegram but this was expensive and considered rather extravagant and usually reserved for weddings or birthday greetings from the Queen. The alternative for most of us was the humble postcard. If there was a quiz or a competition on the TV, it was "answers on a postcard please" rather than a text or call to a premium rate phone number. Postcards were sent to say thank if you had been to someone's house for a meal and they were, of course, sent in numbers from holiday makers in Rhyl or Blackpool or the Norfolk Broads, "Wish you were here". Like a text or a tweet, the postcard was a brief, few word statement, a reaching out to another: I am here, wish you were here, talk to me. It just took longer to get there.

It is the sending of postcards that links the two stories I want to share with you today, fragments of communication from the front line, hurriedly scribbled witnesses to the catastrophic world wars of the last century.

Being able to write and receive postcards was very important to soldiers in the First World War. Of course, some had time and opportunity to write letters but for many it was a postcard hastily written out in appalling conditions. Written to reassure sweethearts, parents, friends, to bear witness and to say I am here, remember me.

This postcard is from Douglas Pym, my wife's grandfather. It is not addressed but it is dated 1914. We think it was sent to Glad the sister of his best pal, Ted. Ted and Doug joined the Middlesex Regiment at the beginning of the WW1. The postcard reads "This is just a few of my company. Please don't be critical". It does show a rather roguish band of soldiers lounging about under the watchful gaze of a splendidly moustachioed Sergeant Major. My guess is that this photo was taken in this country and certainly before the company saw any action. There is a swagger, an insouciance about them

The second postcard is also not addressed. It was made in France and shows a picture of a young British soldier in puttees taken in a photographic studio. The date is October 27th, 1917 and the card reads simply, "To all at home with best love, Douglas". We know that between these two postcards, Douglas has fought in the Battle of the Somme and been taken a prisoner of war. This is a postcard from a prison camp somewhere behind German lines. One sentence was all that was allowed. We know too that his pal Ted, Private Edward Dennis Bristow TF/3479 of the Middlesex Regiment, was killed on 26th June 1916 at the battle of the Somme aged 19.

The final postcard I have here from Douglas is addressed to Miss G L Bristow, 2, St Dunstan's Villas, Hounslow, Middlesex, Blighty. This is Ted's sister, Glad whom, when he returned from the war, Douglas married. It is a photograph of the railway station at Charleroi in Belgium and is dated 22nd November 1918, eleven days after the Armistice. One side of the postcard shows a serrated edge. It was one of tear-off set of cards. "Dear G," it reads, "Just a line to say that I am once again with our army. Have never been to Germany, have been working behind German lines. I am on my way home but cannot say how long I will be, affectionately, Douglas."

Postcards from hell. I am still here, they say. In the midst of all this carnage and brutality emerges that human desire to reach out, reassure. I still exist. I am on my way home. No doubt, in many families here there are bundles of such postcards and letters from the front line, tied up in string, photos, memories, witnesses to the most ferocious and bloody war in human history. These postcards remind us what it is we remember today. The young men who were mown down, brutally treated and the young women who lost bothers and whose sweethearts returned home haunted and broken in spirit. Men who were not martyrs for a grand cause but who fought for their families, their "pals", their sweethearts and for that most powerfully charged word of all, "home". "I am on my way home."

The second postcard is not personal to our family but can be found in a collection of letters written by a young Dutch woman called Etty Hillesum. This card is postmarked 15th September 1943 but we know it was written on the 7th September. Etty herself never got to post the card. It was sent on by a farmer who found it in a field where it had landed when Etty pushed the postcard through the slats of railway truck as it pulled away from the transit camp at Westerbork on its way to Auschwitz. It is the last letter she wrote and this is how it reads.

Christine, Opening the Bible at random I find this "The Lord is my high tower". I am sitting on my rucksack in the middle of a full freight car. Father, Mother and Mischa [Etty's brother] are a few cars away. In the end, the departure came without warning. On sudden special orders from the Hague. We left the camp singing. Father and Mother firmly and calmly, Mischa too. We shall be travelling for three day. Thank you for all your kindness and care. Friends left behind will still be writing to Amsterdam; perhaps you will hear something from them. Or from my last letter from the camp. Goodbye now from the four of us. Etty.

Etty was clever, curious, brilliant. She was also Jewish and she died in Auschwitz at the age of 29. As well as letters from the holding camp at Westerbork we have her diaries for the years 1941-1943. You can get hold of them under the title An Interrupted Life. They are a remarkable record of the life of a remarkable woman. If you get to read the diaries and the letters (and I hope you will) you will be struck by the working of two powerful and opposing forces in Etty's life during these years.

If you know the diaries of Ann Frank you will be aware of how life was for Jews in occupied Holland. Etty records her rich and sometimes wild love life, her friendships, reading matter, thoughts and reflections. She also records the sinister creep of growing restrictions placed upon the Jewish community in Amsterdam. And the reader, who knows how this is going to go, feels the vice closing as the Gestapo first forbid Jews to use certain shops or visit particular parts of town, then require them to wear a star of David, then impose a curfew and then round them up into transit camps from which they will be transported to the death camps. It is suffocating and terrifying.

But in the midst of this horror something else is going on in Etty's life. Her family were not practicing Jews but she finds herself reading her Bible and writers such as St Augustine and the very secular and sceptical Etty discovers herself one day facing a powerful compulsion to fall to her knees to pray. "What a strange story it is really," she wrote, "the girl who could not kneel. Or its variation: the girl who learned to pray. That is my most intimate gesture, more intimate even than being with a man..." In the midst of Nazi horror and kneeling on the bathroom floor in prayer, Etty came to the daring conclusion that she had to, as she put it, "take responsibility for God" by which she meant that she had to show in her life that there was an alternative to the brutality of Hitler and his sick and lethal fantasies. She had to show that the insane cruelty of Hitler was not the final reality of things; she had to make God credible in a world gone mad.

It is hard to comprehend, Oh God what those created in Your likeness do to each other in these disjointed days. But I can no longer shut myself away in my room, God, I try to look things straight in the face, even the worse crimes, and to discover the small, naked human being amid the monstrous wreckage caused by man's senseless deeds

Etty made a deliberate decision to fashion a life based on forgiveness and love and compassion because if she did not this great evil abroad in the world would have won. Just as St Peter characterises Jesus' life from our second reading:

When they hurled their insults at him, he did not retaliate; when he suffered, he made no threats.

It is a different way of fighting the battle, a refusal to give into bitterness and hatred and a commitment to affirming the beauty and love of God amidst all that distorts that love and beauty.

In the camp at Westerbork, Etty could write this:

Sometimes very late, at night, I find myself walking with a spring in my step along the barbed wire. Time and again, this feeling comes into my heart - that life is beautiful and meaningful and, some day we shall be building a whole new world. . . If we just care enough, God is in safe hands with us, despite everything

Ah, yes, "if we just care enough". This what faith looks like, "taking responsibility for God", believing in the possibility of redemption even when all the evidence points in the other direction, trusting that goodness and beauty are not some kind of illusion and working for "a whole new world".

In that postcard thrown from the freight car bound for the Auschwitz, Etty wrote, "We left the camp singing." It takes a certain kind of courage and faith to sing in the face of immense cruelty and barbarism. How easy it is for us, who face no such terrors, to become cynical and weary in the face of our own failures and those of others and yet, "we left the camp singing" and "God is still our high tower". Etty does not pretend that the world cannot be a violent, degrading and frightening place – she knew better than we how it could be full of terror – but she refuses to acknowledge that this is the final word. She is no Pollyanna but neither will she succumb to the sin of despair. Instead she sends out a postcard from the very gates of hell that speaks of the triumph of goodness and the unending song of hope.