Did he set the stage ahead of time so that Merry could use his Barrow dagger to break the spell that made the Witch King invulnerable to mortal men?
Tom went up to the mound, and looked through the treasures. Most of these he made into a pile that glistened and sparkled on the grass. He bade them lie there 'free to all finders, birds, beasts, Elves or Men, and all kindly creatures'; for so the spell of the mound should be broken and scattered and no Wight ever come back to it....
For each of the hobbits he chose a dagger, long, leaf-shaped, and keen, of marvelous workmanship, damasked with serpent-forms in red and gold. They gleamed as he drew them from their black sheaths, wrought of some strange metal, light and strong, and set with many fiery stones. Whether by some virtue in these sheaths or because of the spell that lay on the mound, the blades seemed untouched by time, un-rusted, sharp, glittering in the sun.
'Old knives are long enough as swords for hobbit-people,' he said. 'Sharp blades are good to have, if Shire-folk go walking, east, south, or far away into dark and danger.' Then he told them that these blades were forged many long years ago by Men of Westernesse: they were foes of the Dark Lord, but they were overcome by the evil king of Carn Dûm in the Land of Angmar.
'Few now remember them,' Tom murmured, 'yet still some go wandering, sons of forgotten kings walking in loneliness, guarding from evil things folk that are heedless.'
The hobbits did not understand his words, but as he spoke they had a vision as it were of a great expanse of years behind them, like a vast shadowy plain over which there strode shapes of Men, tall and grim with bright swords, and last came one with a star on his brow. Then the vision faded.... It was time to start again.... Their new weapons they hung on their leather belts under their jackets, feeling them very awkward, and wondering if they would be of any use. Fighting had not before occurred to any of them as one of the adventures in which their flight would land them.