To bathe or not to bathe. That was the question. Here I was, for the second time in Lourdes, and the first time as a pilgrim with my diocese. Last time, I had been too busy reporting on Pope John Paul's spectacular finale to his travelling papacy; now, the queues, at least for the men, were not onerous. The most lourdais of rituals beckoned.

But why do it? The long wait, the undressing, the waiting damply in semi-nakedness, the plunge into freezing water while muttering an Ave Maria—all this, regulars cheerfully admit, is extremely unpleasant. The idea, it seems, is penance.

We Catholics believe in human dignity, but only because we can embrace, like our Master, human indignity.

But not all sacrifices are salvific, a matter which God cleared up when he asked to be excused from tedious liturgies and sacrifices involving the incineration of cattle (see Amos, ch 5 et seq). And I had already done, the day before, a Stations of the Cross on the hill above the Grotto, atoning (yes, in the heat and dust) for my own transgressions and not a few of the globe's.

And just whose idea was it, this ritual? Our Lady asked Bernadette to "go drink at the spring and bathe in its waters", but "wash yourself" is just as good a translation, and rather more easily carried out under one of the grotto taps with a few wet slaps on the cheeks. And what of Our Lady also instructing Bernadette to kiss the ground and eat the grass? Only popes do the first, and no one ever suggests that pilgrims to Lourdes should chew the fields.

But then I pondered the story. The earth, when Bernadette obeyed on 25 February 1858, was muddy; the grass was bitter; the water brackish. Onlookers who accompanied her up to this, the ninth apparition, were appalled to see her scratching the ground and acting like an animal. If these were the scandalous instructions of the Mother of God, for which she was slapped and led before the Public Prosecutor, who was I to object? The message transformed the young asthmatic seer, who thenceforth began to pray for the conversion of sinners.

Self-abasement, after all, is God's chosen method of saving humanity. We Catholics believe in human dignity, but only because we can embrace, like our Master, human indignity.

I was wobbling, you see. And then, over a biere formidable, I had found myself convinced by Fr Chris Vipers, the diocese's charismatic Lourdes pilgrimage director.

"It's about becoming a child again," he told me. "Trusting others. You're naked and dependent, at that moment, on others to hold you and immerse you. It's about admitting your vulnerability. It's about trust. And surrender."

You’re naked and dependent, at that moment, on others to hold you and immerse you. It’s about admitting your vulnerability.

The prototype Gospel of Lourdes is Luke's account of the paralytic being lowered through a roof by his friends into the healing presence of Jesus. That is how the sick come to Lourdes—with enormous difficulty, carried by others, trustingly. But not long is needed to realise that what the malades accept, as it were, faute de mieux, is what the rest of us pilgrims are invited to embrace too, spiritually speaking. Healing happens when, like Bernadette, we put aside our ego-armoured selves and trust in our Creator. Hence the baths: they have emerged, over time, as the essential physical ritual of Lourdes, one that opens the heart and mind to grace. The bath is not a sacrament, but it is sacramental, an act of immersion in much the same way as the Eucharist is an act of incorporation.

Thus theoried up, I found myself queuing in the hot sun, elbowed by Italians even shorter than me, and then shuffling along a bench which snaked round towards the entrance of the baths. Every time eight men disappear inside we move closer, in the manner of an old-fashioned confessional queue. The malades, along with the clergy, are fast-tracked in: they enter on crutches and in chariots, in the company of cheerful hospitaliers.

Gloria patri et filio ...

Here we all are, some sixty men from the Euro-Catholic belt, mostly middle-aged, but a smattering of young, grunting the rosary, staring at our feet as if awaiting a test for testicular cancer. In 2004, more than twice as many women (266,583) as men (121,715) took up the Virgin's invitation. Hence the disparity in facilities: there are 17 baths in total: 11 for women and 6 for men.

A paralysed man, it occurs to me, cannot move, but he is far from passive. He can refuse to be moved, or he can ask to be. We are all paralysed and crippled by our self-righteous autonomy. We all need to trust, to let ourselves be moved, to allow ourselves to become dependent.

Prima volta? I ask my Italian neighbour. He came once before, 15 years ago, he tells me. Right now, twice in 15 years seems excessive.

A boy on a stretcher-chair has his hands in the air, twisted grotesquely in the classic sign of the severely disabled.

Laudate, laudate, laudate Maria, a man is urging us to sing.

"What language is that?" an Englishman behind me asks.

"That's Latin," his friend ventures.

"Oh, really?"

Our literal age has little time for this stuff, which shrivels under the cold glare of rationalism. But the sacramental imagination is bigger, deeper and wider.

The stretcher carts are lined up now, contraptions from a bygone age. One is occupied by a very frail old man, his hands purple and gnarled. As the rosary switches to German, one of our number bottles out, leaving quickly, shame-faced. Perhaps he has lost touch with his inner child. I am tempted, for a moment, to follow him. This trust stuff is demanding.

Hell Merry, fool of grease, zee lawd is weez you, comes a voice over the loudspeaker.

"Is that Latin too?" the voice behind me asks.

"No, I think that's English"

"Oh, really?"

Out comes a Down's syndrome boy, face creased with smiles. He gives us all a thumbs-up. Nothing to worry about, fellahs, he seems to say.

The Catholic Church is nowhere better represented than here, at this moment. The boundaries between physical and spiritual are collapsed, and the Kingdom breaks out: the disabled mingle with the able-bodied, the nations mix, and we tap into God's goodness by physical acts which we are confident are not meaningless. Our literal age has little time for this stuff, which shrivels under the cold glare of rationalism. But the sacramental imagination is bigger, deeper and wider.

All I have done is move down a pew or two, but I am much closer to what this is all about. Our unconscious grasps what our eyes cannot. Who are they, in the chariots in front of us now? Our fears—deformation, paralysis, fragility—but also our glory: the Spirit of God, assuring us of human empathy and supernatural transcendence. Healing is collective; we are in need of others. The fellow in the middle with the purple fingers could go at any time, but what better way than like this, carried by gentle young helpers, into the arms of God?

A young Westminster priest sits on the fast-track clergy bench. His open breviary reminds me to stop taking notes and be present to the moment. There is a sliver of ice in the heart of every writer, Graham Greene once said—and he should know. So I melt mine by pondering my intentions: a friend's imminent baby; frail and elderly relatives; a despairing friend.

"Any tips, Sean?" I ask a friendly "Red Cap", as the wheelchair-pushing volunteers are known.

"It's humiliating and unpleasant," says Sean, grinning. "But think of the fact that since the 1850s millions of people before you have done the same. And you're somehow connected with all of them."

Inside, my parish priest leaves one cubicle and a finger protrudes from the next one, motioning for me. Four young men in blue overalls—brancardiers in the Lourdes argot—and four men sitting in their underpants on chairs. I get the idea, and divest. An elderly man in a wheelchair is brought in. "So what we're going to do," the English broncardier gently tells him, "is to remove your shoes and socks. Then your trousers. Then your shirt." He taps each of the articles. "But we're going to leave your underpants on—for the moment."

In the chair next to me, an old man is asked if he wants just to be splashed, or dropped all the way in.

"I've been coming here since 1950," he answers, blimpishly. "I want to go right in. All the way."

Right in? All the way? How deep is this thing?

The wheelchair-bound man was gently disrobed, until all was left were his underpants and a catheter tied to a bag of urine strapped to his pallid, blue-veined left leg. I shuddered for a moment at the description of the bath water in Lourdes, Emile Zola's bestselling anticlerical tract.

As some hundred patients passed through the same water, you can imagine what a horrible slop it was at the end. There was everything in it: threads of blood, sloughed-off skin, scabs, bits of cloth and bandage, an abominable soup of ills ... The miracle was that anyone emerged alive from this human slime.

Healing happens when, like Bernadette, we put aside our ego-armoured selves and trust in our Creator.

My turn. A deep stone bath, tiled in the Virgin's blue, with (phew!) clean water, all overseen by the Immaculate Conception. Three more broncardiers. Turn to the wall, I was told, and remove your underpants. As I did so, a freezing wet towel was put round my waist. The shock of the cold made me turn round too soon, and a broncardier to shield his eyes in mock horror.

I stepped in, and was told to make a prayer to Our Lady. A humble child I was; defenceless, powerless, borderless. A moment of great psychic and physical vulnerability, but I trust these strangers.

I rattle off a Hail Mary, forgetting my intentions.

Arms grip me. Down I go. Splash—the shock of the cold. Then up. Pants back on. Out. Change. No towel, because by tradition the water is deemed unwet.

Back into the sun, and the pious chaos of the Grotto. I find a patch of sun-kissed grass. The water has dried, soaking me in peace.