There’s no word in Scottish Gaelic for “moreish” – or if there is, it slips Rob MacNeacail’s mind as he reaches for another biscuit in a church hall. MacNeacail is a Gaelic psalm singer and the eccentric star of this gentle and rather lovely film from Jack Archer that follows him on a mission to meet other singers keeping the tradition alive. Not that you’ll learn an awful lot about the history of psalm singing from this film; it is essentially an observational portrait of MacNeacail, at his home on the Scottish borders then out on the road to the Outer Hebrides, Skye, Belfast and County Cork.

But no knowledge is necessary to enjoy the extraordinarily rich and textured sound of psalm singing, once practised at Free Presbyterian churches all over Scotland. It’s a community activity: one person – the precentor – sings a line of a psalm from the bible, and everyone else sings it back slowly, each with their own interpretation, at their own tempo. No instruments, just voices; like the sea, the sound comes in great swells and then retreats. It’s haunting; shut your eyes and you might be in a stone chapel in the 1800s.

It’s a form of Christian worship, but MacNeacail’s interest seems to be cultural; his father was the poet Aonghas MacNeacail who wrote in Gaelic and died in 2022. The immensely likable MacNeacail explains how Gaelic words will sometimes knock the English version out of his mind: “I am being decolonised by my own brain!” His day job is working at a care home for adults with learning disabilities, where one of the residents is his sister Galina; they clearly adore each other. On his travels, MacNeacail’s warmth and humour shine. On the Isle of Lewis, he sings with Gaelic psalm singing expert Calum Martin. “It’s like meeting Yoda!” MacNeacail exclaims. He is a pleasure to watch, and surely this worthwhile film will help psalm singing survive.

• Sailm nan Daoine (Psalms of the People) is in UK and Irish cinemas from 15 May.