Old Firm friends or bitter rivals... either way, they are what keeps us all watching
No one at Celtic will admit it publicly, but the simple truth is that the Scottish game will be much better off - both financially and competitively - if Rangers win their play-off tomorrow
Almost exactly 127 years ago, a football match took place in the East End of Glasgow. A rather homespun affair, between two teams coming to terms with the birth of the professional game in Scotland.
"They got on so well that you would believe that they were old firm friends," one commentator noted. And, following Celtic's 5-2 victory over Rangers, a toast was made from the Celtic board to "our friends, the Rangers".
Minus foresight, who among the convivial gathering was to predict how these hopefuls would end up fuelling global fascination in what is, arguably, still regarded as the world's most famous derby encounter.
It was the Parkhead club's first-ever game, while the Light Blues were already up and running from 1872. As commercialism took hold, so divisions, inevitably, emerged between Glasgow's growing duopoly.
Money was to be made and, over the years, the developing tribalism between the pair suited both, even if club overlords - Bill Struth of Rangers and Willie Maley of Celtic - enjoyed a warm friendship.
Much more recent history has proven to be an unprecedented saga, however, with Rangers coming to terms with awful mismanagement, administration and demotion since early 2012.
The sight of this proud outfit - a traditional bastion of old-world Scottish Establishment values - hauling themselves up from the depths, at places like sea-swept Arbroath and Stranraer, was particularly surreal, both for Rangers fans themselves and those who, frankly, revelled in their misfortune. There isn't much wrong with that; the game sometimes thrives on the edge of hostility.
Yet, when you oversee the downturn in Scottish football since the Ibrox club's shock demise, the jokes now seem as weary as Rangers' turgid performance on Thursday against Motherwell in the first leg of the Premiership play-off final.
Can Stuart McCall's men overturn a 3-1 deficit at Fir Park tomorrow? Failure to do so could cause massive psychological carnage at Ibrox.
It's not just Celtic who should be relieved, if Rangers carve out a heroic success. The SPFL itself has only managed to secure a new sponsorship deal with Ladbrokes, following two barren years.
It has been a hard commodity to sell, not just to supporters in Scotland, but worldwide, without this most colourful of unique selling-points.
Notwithstanding the shortcomings in actual playing quality, the Rangers-Celtic clash is enviable theatre. While regularly lacking finesse, few games in world football - England included - can compete.
The high-water mark of modern era exposure for both clubs was at the turn of the millennium, when Rangers had stars such as Ronald de Boer, Giovanni van Bronckhorst and Barry Ferguson, with Henrik Larsson, Stiliyan Petrov and John Hartson thriving under a Martin O'Neill-inspired Celts.
Back then, people took notice. Clearly, diluted finances don't stretch to the de Boers and Larssons these days. Nevertheless, there is scope for a better-packaged product - but it must include a competitive Rangers to stretch the Hoops.
Celtic chief Ronny Deila would relish the test and, it's worth remembering, without the Glasgow derby to stir the blood, predecessor Neil Lennon became weary as the old noise and colour he loved faded away. Stefan Johansen - Celtic's star this season - presumably has the Old Firm "experience" on his wish-list, too.
Moreover, why else do Rangers supporters still rock up to games - with average attendances of more than 45,000 - to watch a side which is probably the worst in club history?
Of course, you must account for sheer defiance. But it's more than this. The large numbers from Northern Ireland, for example, who continue to visit Glasgow to watch veteran Lee McCulloch labour against Cowdenbeath do so in the belief that they are part of something greater than a club. In Rangers' case, it does go beyond the cliche.
There is a wonderful photo of the Rangers Accordian Band taken in Belfast in 1961 ahead of a trip to Scotland to see the legendary Jim Baxter in action; echoes of the era of migrant Ulster shipyard workers to Govan, as the nearby club reigned under Struth's highly-successful benign dictatorship.
In spite of occasional dismissive noises from liberal elites, there is a long-accepted view that Rangers - like Celtic - are enormous components of Scottish society. They lubricate the passion for the national sport, in spite of occasional unsavoury, but fortunately receding, bouts of sectarian behaviour.
The elephant in the room is that the Scottish game is not realistically big enough, or rich enough, to withstand Rangers' prolonged absence and expect to thrive. As Celtic discover over the course of a league campaign, others - Aberdeen, say - challenge, but they lack the stature, depth of squad and finance to last.
Meanwhile, the more objective at Parkhead seek a return to the traditional battlefield. Dermot Desmond, Celtic's majority shareholder, noted in the aftermath of the Ibrox meltdown, "Rangers are a fantastic club with a great history. They will, in not too long a time, be back. I have no doubt about that. And they're needed for Scottish football, because of their following, the size of the club and especially their history."
Unsurprisingly, such views were poorly received at Celtic Park grassroots, but he was on the money. And Celtic have always known the value of thick coin, particularly when Fergus McCann swept into power during the club's darkest hours in 1994, to drive home frugal mindsets and fresh ambitions.
For Rangers, their troubles are unique and deeply complex. As new director Paul Murray said recently: "The club is broken". The team itself may be poor, but the financial muscle Rangers fans bring can assist other clubs, with many stadiums hosting games in front of swathes of empty seats. Scottish football requires fixing, too, but the symptoms can be treated.
Rangers may have been wrecked from within by Sir David Murray's spendthrift folly and the disgraced Craig Whyte's failure to pay as you earn, yet it's still only seven years since Walter Smith guided the club to a Uefa Cup final.
That, plus Celtic's occasional capacity to clip the wings of Europe's fashionable elite, indicates a potentially strong Old Firm can greatly enhance Scotland's sense of itself.
Hearts - winners of this season's Championship - have impressed with their cost-conscious, youth-driven, action plan. They, along with Aberdeen, can test Celtic to a certain extent next season. Rangers have far more to do.
As a club, they are still raking through damage inflicted by previous irresponsible owners. Temporary coach McCall is unsure if he will remain at the helm, although at present, there is a temptation to retain his services. It may not, though, satisfy a still-ambitious support craving a fresh face to lead them out of the wilderness.
Memories of Ally McCoist's burn-out are stacked against McCall, regardless. With an old boy mentality comes complacency. McCoist will always be an iconic figure for his goalscoring feats and public representation of Rangers in the dark days, post-administration, but he was not the ruthless, experienced managerial figure required for a complete overhaul. Big wages to old SPL sweats raking around lower leagues highlighted a desperate lack of imagination.
If new chairman Dave King purges the commercial headaches linking minority shareholder Mike Ashley to the club, Rangers can inch forward. Still, the removal of the Sports Direct tycoon is going to be complicated business, adding to concern of falling attendances if the team flops at Motherwell, to be consigned to another Championship term. As ever, the ferryloads from Northern Ireland will be called upon again.
The immediate future? An end to veterans Kris Boyd, Kenny Miller and Lee McCulloch slowing down progress. An end to controversial, cheap sales of bright prospects, such as Lewis Macleod, mid-season. An end to the assumption that a vast fan-base will continue to indefinitely accept agricultural tactics. McCoist's flippant approach grated. If McCall remains he dare not make similar mistakes.
An expansive style, focusing on youth - as in Hearts' case - is paramount. McCall did a decent job in reduced circumstances at Motherwell before accepting his temporary Ibrox firefighting role, but he is not a visionary.
An idle thought, perhaps, but maybe the Gers require "their" version of Ronny Deila: an objective figure to inspire. The Govan outfit are "broken" but they retain a cachet and the restoration of fortunes is an enticing opportunity, albeit on a minor budget.
From the oak-panelled surroundings of the Ibrox Blue Room, King needs to view through a wider lens. He can take the supposedly "safe" option in former player McCall, or he can discreetly invite applications from the ambitious.
With the Scottish game at a crossroads and Rangers muddling, in a sense both tribes have lost sight of each other. These days, Light Blues' fans tend to ignore much of the goings-on across the city.
Deila's men have won their fourth successive title, the Norwegian carrying on Lennon's good work. For Rangers, though, it's an irrelevance, particularly if they fail at Fir Park.
Racked by fear during the first leg, McCall is demanding an extraordinary response. Ninety minutes in Lanarkshire will make-or-break Rangers' immediate fate.
SPFL clubs, their accountants - and possibly certain old friends - await with interest.