The religion of the Druids of Caledonia differed in some degree from that of the Druids of Britain. The people were taught to worship the sun, the rivers and the forests. Certain of the streams and wells which were, said the Druid priests, under the influence of a beneficent spirit, were wholesome and good to drink, while to taste of others which they declared to be under the rule of evil spirits, would be followed by instant death.

The first thing to be done was to convince the people of the falsity of their belief and to make them cease the idolatrous practices connected with it. Columba drank in their presence of the water that was supposed to be deadly, to prove to them that no evil effects would follow. The Druids pursued him wherever he went, interrupting him continually in his preaching, holding him up to the derision of the people, and misrepresenting what he said. Columba bore all their insults with patience; but when it came to trying to drown the missionaries' voices in the singing of the psalms of the Church with shouts and mocking cries, his zeal for God's glory overcame for once his meekness, and he intoned the holy chant in such a voice of thunder that his adversaries were silenced, and the King and his people trembled with fear.

In spite of the Druids, crowds flocked to hear the preaching of Columba, and many were converted to the faith. On one occasion, shortly after the conversion to Christianity of a whole family, the eldest son fell ill and died. The Druids were of course at hand to assure the sorrowing father that the loss of his child was a well-merited punishment indicted by the gods of his country in consequence of his apostasy. The man's faith wavered, but Columba was watching over his converts; and after doing what he could to console the grief of the boy's parents, asked to be left alone beside the bier to pray. With tears and entreaties he besought of God to show forth His almighty power, and the Heavenly Father heard the prayer of His servant and raised the child to life. Columba led him to his parents, and their faith in the true God was confirmed for ever. The prayer of Columbcille, says Adamnan his biographer, was as powerful with God as that of Elias and Eliseus in the old law, and Peter, John, and Paul in the new.

One day when the Saint was preaching the Gospel in the island of Skye, he had one of those flashes of supernatural insight of which we have spoken several times before. He told his companions that there would come to them that very day an old Pictish chief who was at the point of death, and who had tried to lead a good life according to the natural law of God and the light of his own conscience.

It happened as he had foretold. Towards evening a boat was seen approaching the coast of Skye, manned by Pictish warriors supporting in their arms an old man whose trappings proclaimed him to be of noble birth. Drawing their boat to the shore, they landed and formed a rude litter with their shields, on which they carried the old chieftain up the hill and laid him down at Columba's feet. The Saint spoke to the dying man of the faith of Christ and baptized him, and shortly afterwards he gave up his soul to God.

On another occasion when they were crossing the mountains, Columba saw a vision of angels, and exhorted his companions to hasten on their way. "For," said he, "there is a man of good and honest life waiting beyond the hills to receive baptism before he dies." They quickened their pace, and when they reached Glen Urquhart, found, as Columba had predicted, an old man awaiting their arrival. The holy abbot baptized him and bade him depart in peace, and the angels whom he had seen on the mountains carried his soul to heaven.

The chief Druid Broichem had a young Irish slave-girl, taken captive in time of war, for whose freedom Columba had several times petitioned. The Druid, who was not likely to look favourably on any request of the great Christian missionary, even refused to accept the ransom offered for the girl, though she was pining her heart out for her family and her home.

Columbcille warned him that if he persistently refused to show mercy to his captive, the punishment of God would overtake him, and he would die before Columba himself left the country, but Broichem was not to be moved. Not long afterwards Columba set out on his return journey to Iona, but he had hardly reached Loch Ness when he was overtaken by two messengers from the high-priest beseeching him to take pity on their master, who had been suddenly taken ill and was in danger of death.

They were assured that the Druid would recover, but only on condition that he set the Irish maiden at liberty. She was at once sent to Columba, who found means for her return to her country and her people. As for Broichem, he was more incensed than ever against the Christians, and considered how he could best check their growing influence with the people.

The Druids seem to have had a certain power over the elements, perhaps through the evil spirits whom they worshipped. They had heard of and seen the miracles worked by Columba, and resolved to show how superior their powers of magic were to his.