“MY happiness is to think of you and to love you. You always brought me more. You were the chance of my life.” These words, written four months before Francois Mitterrand's death in 1996, formed part of the former French president's final letter to his lifelong lover, Anne Pingeot. Despite the near 30-year age difference (she was 19 when they first met, he was 46 and already married with two teenage sons), their love affair spanned 35 years.

The letters – all 1,200 of them – were published last week to coincide with the centenary of Mitterrand’s birth near Cognac in France. Often referred to as the Sphinx, his political persona was Machiavellian, highly controlling and ambiguous. But there is no trace of ambiguity in the letters to Pingeot. They are ebullient, intellectual, deeply intimate and spiritual affirmations of his love for her.

These are proper love letters where there is no holding back. In true Baudelairean fashion, Mitterand pours out every last drop of longing and desire, leaving Pingeot in no doubt about how loved she is.

Imagine if Mitterrand had sent texts instead of letters, or just composed his love missives on a computer and sent them as email attachments, Somehow, they wouldn't have had the same allure, intensity or, indeed, posterity.

Letter writing is a dying art. When was the last time you sat down and absorbed yourself in writing to someone you loved about something that really mattered to you? Virginia Woolf, a masterful, generous and lifelong letter-writer (who ended her own life with a letter before her suicide in 1941) saw its demise as far back as 1940 when she fretted over the increasing use of the "telephone and the wireless". The fact is that most of us are too busy multi-tasking and staying "connected" to commit ourselves to pen and paper to make a real connection through the gift of a handwritten letter. A good letter is one that is written from the heart and mind. It will be kept by the recipient, curated with other significant memorabilia in an old shoebox or at the back of a drawer that nobody else uses. Rarely, will it be thrown away or, in the case of texts or emails, deleted when your device memory gets too full or blasted into cyberspace. A good letter will be read and re-read. There may be gulfs of years between each reading, but as we age, we understand the words differently, their meaning filled out by the passing of time, the living of an imperfect life.

In this sense, letters are dynamic and revitalising. They may evoke feelings in us that are raw, painful or even shaming (perhaps because we did not reply or because we were too young or self-absorbed to empathise with the pain of another).

We can say things in letters that cannot be said in any other realm. We can express gratitude to someone who has cared for us, inspired us, or even saved us from a fate worse than death. We can explain to an adult child the reasons why, as parents, we may have let them down, not expressed our love enough. We can share personal history that throws light on the darkness of the past. Or we can give an account of why we made the choices we did and acknowledge their impact on others.

The letters we write tell the recipient that they matter to us. Texts are 10 a penny, usually composed on the hoof with minimal presence of mind. They are reactive and very often mindless, borne out of boredom, emptiness, an unsettling hiatus in frenzied displacement activity. The longevity of a text endures just about the same length of time as it takes to read it, then it's gone forever to the cyber-cemetery. Letters, on the other hand, stick around. We can hold them in our hands, observe the pattern of the handwriting, consider the use of punctuation, how words are spelled or misspelled. All these are clues to the character and personality of the letter-writer, their mood at the time of writing, their feelings about us and about themselves.

Most of us have a letter we need to write. Most of us put it off, telling ourselves that it's too "heavy", too revealing or we don't have time. We’ll do it when we next have a day off or when we've re-tiled the bathroom. It is letters such as these – unwritten, past due and suspended in our minds – that really need to be written.

Whether it's a plea for forgiveness, a striving to understand someone's actions or just a fervent, unedited declaration of love and joy, that letter will make a difference to you and the recipient. It becomes not only an artefact of authenticity but a living, breathing connection here, now and in a future that is not yet born.