Howard Jacobson: Thanks to Leonard Cohen, I can see the light that slips through the crack

These have been a serious few weeks, our country locked in profound moral debate about aesthetic judgement versus popular appreciation, the boundaries of good taste, the rights and wrongs of telling radio audiences whose granddaughter you've been knocking off, the case for universal suffrage when it comes to deciding who should win The X Factor or remain on Strictly Come Dancing.

Anyone just landed from Mars watching John Sergeant's farewell dance to a standing ovation of solemn tears and eulogy would have supposed we were saying goodbye to a leader who had led us through war, famine and the plague. Certainly Sergeant spoke to the nation as though he'd done that and more. Those whom the television gods would destroy they first make vain.

What Sergeant forgot was that he'd entertained us because of what he couldn't do, not because of what he could. Incompetence is a great virtue to the English, but only so long as it's wedded to modesty. Imperfection with no delusions is what we like.

"Ring the bells that still can ring" is my motto. "Forget your perfect offering – there's a crack, a crack in everything." I have, of course, stolen those words from Leonard Cohen. Why not? In complex moral times we need whatever guidance is on offer.

Leonard Cohen isn't somebody I'd put my mind to much until the other week when I went to see him at the O2 in Greenwich. I and 50,000 other people, not doddery exactly, but not of an age to pull a knife whenever someone disrespected us by breathing in our direction. Not the same audience, in other words, as attended the Urban Music Awards the night after. Trouble waiting to happen, if you ask me, the minute you call something Urban Music. What's in a name? Everything. Urban is a moral anagram of armed. But who's going to come jingling weaponry to an evening entitled Leonard Cohen? You would as soon take a gun to a bar mitzvah. We, anyway, were just there for the words, the music and a dollop of nostalgia. Is that why the urban young are so jumpy – they don't have enough to remember? Certainly there's less room for knives if you're loaded down with recollection. And of course you move more slowly.

I read Leonard Cohen with passing interest, in the 1960s. I liked a number of his poems whose names now escape me and was aroused by his novel Beautiful Losers, described by someone as the "most revolting novel written in Canada", a compliment it's hard to gauge until you know what other revolting novels have been written in Canada. I could suggest a few but this isn't a provocative column. After Leonard Cohen I'm in beautiful loser spirits – "Dance me to the end of love" spirits, decadently moony, feeling it's all over but still hoping for another chance, "For flesh is warm and sweet". Sound a bit 1960s? Well there you have him. And there you have me too.

Post the 1960s, when he started to put his poems to music, I fell out of interest with him. Singing, singing, singing – why had everyone suddenly burst out singing? Thereafter, since I wasn't a buyer of albums, I lost track of his career, didn't know if he was alive or dead, couldn't remember a line, even of the most revolting novel ever written in Canada, and never expected to think about him again. Now here I am in his audience, and now here he is, a devilishly attractive man in his middle 70s. Some men do old age better than they do youth. Especially melancholy-sensual men who can't decide whether they're happy or not. The not knowing, like the not eating, keeps them lean. He is fascinatingly attenuated, as laconic as a snake on grass, with a face lined by a lifetime's amused and desperate indulgence of the appetites, by which I don't just mean wine, women, infidelity and betrayal, but also rhapsodic spirituality alternating with ecstatic doubt. A meanings man. It's corny in its way, as well as beautiful. All existentialism when its lifestyle is corny. But there's a crack, a crack in everything. And you won't be popular unless you're corny.

I like it that he doesn't jig about. Such a change to see someone on a stage, immobile – as still as thought. We have the attention span of children. A thing will interest us only if it sparkles and moves. Madonna, Michael Jackson – people come back from their concerts raving about how well they move as though moving is a virtue in itself. I don't get it. If you want moving ring Pickfords. Leonard Cohen barely stirs, limiting himself to crouching over his microphone into which he whispers with hoarse suggestiveness. When he does essay a ghost of a dance he gets an affectionately ironic cheer for it.

I would have wished the audience to follow his example. It's all a bit cultic for my taste, fans whooping and waving like born-again Christians at a hymn singing hoedown whenever he starts a song they recognise. I'm thinking about this, wondering if they'd be whooping if he hadn't put his poetry to music, wondering why the words alone won't do, when I hear those great lines from the song "Anthem". Ring the bells etc. Forget your perfect offering. There's a crack – a crack in everything.

It's like a reprimand to people of my temperament – life's complainants, eroticists of disappointment, lovers only of what's flawless and overwrought. Could he be singing this to me? You expect too much, mister. You are too unforgiving. Not everything works out, not everything is great, and not everyone must like what you like. I've been taught this lesson before. I remember reading an essay by the novelist Mario Vargas Llosa in which he argues for the necessity of vulgarity in serious literature. Thomas Hardy said a writer needed to be imperfectly grammatical some of the time. Mailer told an audience that not everybody wanted to ride in a Lamborghini. And now here's Leonard Cohen saying the same thing. Forget your perfect offering. There's a crack...

And then comes another, still more wonderful, clinching line – "That's how the light gets in." Savour that! At a stroke, weakness becomes strength and fault becomes virtue. I feel as though original sin has just been re-explained to me. There was no fall. We were born flawed. Flawed is how we were designed to be. Which means we don't need redeeming after all. Light? Why go searching for light? The light already shines from us. It got in through our failings.

Had I known how to whoop I'd have whooped.