Beginning yet another British tour, with only the Attractions keyboardist Steve Nieve for accompaniment, why should anyone still love this ageing merchant of bile? Two-and-a-half hours after he takes the stage here, as the crowd still roars for more, that question is humbly withdrawn.
This hometown crowd was always going to be a help. Costello and Nieve, in casual black suits, throw them an early bone, "Accidents Will Happen", then settle into the Costello-Bacharach songbook. Costello stands hand in pocket like a suave Elvis who might have written these songs in 1964. Even when he slips into a rearranged "oldie", "Temptation", he sings as a wiser, older man. The vitriol, intensity, and uproar which once marked his shows are gone.
It's hard to know when we all start to see things differently; when the passion returns. Perhaps it's when his lips roll back in his former mannered sneer, a rusty blade unsheathed on "This Year's Girl". Perhaps it's when he follows it with a hushed, intense reading of his great song of spent lust, "Indoor Fireworks". I'm almost sure it's the unrepeatable moment when he breaks off "God's Comic" to improvise a conversation between himself and a god who mistakes him for that other Elvis.
That's when the spark catches light. "Veronica" soon follows, and then "Alison"? He must have sung it thousands of times, but his delicacy and commitment in teasing out its sadness tonight is a wonder that brings tears to the eyes.
At some point, the encores start, the crowd leaves its seats, and Costello realises he doesn't want to stop. When "Shipbuilding" starts with the words "Is it worth it?", someone yells "Yes!", before its Falklands context is remembered and everyone stands as if at prayer. And, at the very last, after signalling "one more song" over and over, and always finding room for another, Costello turns all the mics off and walks the stage, singing his most beautiful melody, "Couldn't Call It Unexpected No 4", to each part of the hall in turn. It's a moment of pure communal connection, something corporate pop culture can't erase. Everyone's faith has been repaid.
Elvis Costello plays Glasgow's Royal Concert Hall on Friday