He created images of lost souls aimlessly circling in sulphurous heat, desperate to have their past sins purified so they could move on to somewhere more tranquil.
With adulthood, I shed my choirboy innocence and his dire warnings were forgotten. That is, until recently, when once again his visions of eternal damnation loomed starkly in front of me.
Purgatory has finally arrived for this lost soul on Saturday mornings, when I'm rudely woken before dawn and commanded to take my children to a stifling heated enclosure, reeking not of sulphur, but the next best thing: chlorine. This is the place where people - mostly fathers, the principal sinners - gather to aimlessly circle in a swimming pool, clutching and dipping their little ones as the prelude to water confidence.
Welcome to stage 1 of purgatory.
As one's offspring become efficient little swimmers, the ritual expands, year in, year out.
In summer it's unbearable, sitting on the sideline, putting up with the heat and the smell of chlorine, but not allowed to join the budding swimmers in the pool.
The 9-year-old has been upgraded to competitive training, and the 3-year-old is still at the tadpole stage.
With purgatory stretching out for at least another decade, it's difficult for this wretched sinner not to fall on his knees seeking mercy.
But the caregiver assures me I'm getting off lightly. For many sinners, the ultimate purgatory is standing all winter on muddy, windswept sports fields watching small children kick a ball around.