IT says something about the eternal quality of the movie Casablanca that it was shown on TV across the channels no fewer than three times on Christmas Day.

I didn’t myself get to watch it this time round. Like most of us, I had just a few other things going on. However, even on Christmas Day, there would be worse ways to spend 100 minutes than admiring the craft of one of the greatest motion pictures of all time.

Everything about the movie oozes quality. The magic chemistry of Humphrey Bogart and Ingrid Bergman, the class acting of Claude Rains, Paul Henreid and Conrad Veidt, backed up by a cast steeped in the best of the golden age of Hollywood. When screen legends such Sydney Greenstreet and Peter Lorre are restricted to just a few lines, it demonstrates that, just as in a fine football team, the Casablanca squad has strength in depth. You can always tell a truly great movie by the quality of the supporting cast.

The lines from Casablanca are Hollywood’s equivalent of Shakespeare or Burns and are among the most quoted of all time. “Here’s looking at you kid”, “play it Sam”, “round up the usual suspects” and “we’ll always have Paris” have been recited by generations who perhaps have never even watched the film.

Casablanca is ostensibly a love story – or, more accurately, two love stories featuring one woman – set against a backdrop of a world broken and in chaos. The characters are deeply flawed or wounded and they merge perfectly into the seedy environs of colonial North Africa, the Vichy-controlled city of Casablanca in 1941. Just about every single character in the movie has either something to hide or something to fear and in most cases both.

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However, Casablanca is about a bit more than that. The film is really on the struggle between good and evil and the realisation that to halt the march of evil it is required not only for good people not to look away, but for less-good people to be prepared to take a hand, to embrace the concept of self-sacrifice. It takes sinners as well as saints to keep true evil from triumphing.

Casablanca is not the greatest film of all time, although it would comfortably make most people’s top 20. It does, however, contain probably the most effective scene in movie history in the celebrated “battle of the anthems” set in the atmospheric surroundings of Rick’s Bar.

In this sequence everything changes. The German officers under Major Strasser (Veidt) break into a chorus of the marching song “Die Wacht am Rhein”, much to the sullen fury of the predominately Free French clientele.

As the singing starts, saloon keeper Rick (Bogart) is in the process of telling his love rival and resistance hero Victor Laszlo (Henreid) that he will not give him the letters of transit, the key to his escape to America to aid the cause of freedom. Rick’s bitterness and cynicism just won’t allow him to do the right thing.

On hearing the Nazis singing, Laszlo marches up to the club band and demands it plays La Marseillaise. The musicians, after crucially getting the nod from Rick, duly do and the crowd lustily stands and joins a united nations explosion of French patriotism. After a few moments when the two anthems struggle to compete, Strasser and his gauleiters are drowned out and sink resentful and defeated into their seats. Having been given just a glimpse of freedom, Ricks Bar erupts into wild celebration.

I defy anyone to watch this sequence without a tear in the eye or a heart beating faster. It becomes clear that the films most compromised characters – the corrupt police chief portrayed by Rains, the saloon bar girl Yvonne played by Madeleine Lebeau and Bogie’s Rick himself – may, when the chips are really down, do the right thing and do it regardless of personal cost. The film then picks up pace to its unforgettable and incredibly romantic conclusion.

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Adding to the scenes emotional power was the decision of producer Hal B Wallis and his friend and director Michael Curtiz to cast European emigres as the extras in the “battle of the anthems”. Indeed only a handful of the entire cast of Casablanca were native-born Americans. Thus the bulk of the bar crowd bombing out Vive La Liberté in the film were real-life refugees from Nazism and, since Casablanca was shot in 1942, in every sense they did not know how the plot would finally end.

So what does this bit of festive film hokum have to do with Christmas or indeed Scotland. The first is easy. What is the Christmas message if not about hope and the reality of self-sacrifice at the centre of the order of things?

The second is more challenging, except for this. Scotland right now badly needs someone to pick up the baton and tell the band to strike up La Marseillaise.