The Seafarer is a big play set in a little room. Comprising nothing more than the banter of old friends (and one diabolical houseguest) in an Irish basement on Christmas Eve, it warmly and humanely paints its characters' portraits as completely as any play can: their histories, flaws, world views, and most private pains. Its playwright's eternal muses are grief, guilt, and redemption, but The Seafarer goes much further. In a sustained moment of uncharacteristic kindness, McPherson wrote his Christmas story as an ode to unconquerable fraternal love — a love that remains strong even when battered senseless by (literally) the forces of hell. It would be difficult to imagine McPherson's script brought off more beautifully than it was at Mosaic Theatre last fall. If you went, you experienced mirth, dread, joy, sorrow, and a kind of moral clarity that you might call "enlightenment" — a stuffed-stocking bounty of thoughts and feelings greater than any piece of art is obliged to supply and which Mosaic nevertheless graciously proffered.