About the close of the sixth, or the beginning of the seventh century, missionaries began to issue from the cloisters of Iona, carrying the light of Christianity not merely to the different parts of Scotland, but to England and the continent. Augustine and his Italian monks landed in Kent a little before the famous Aidan from Iona and his monks entered Northumberland. Thus was Saxon England invaded by christian missionaries at its two extremities.
Oswald, then king of Northumbria, was a Christian. He had been converted, baptized, and received into the communion of the Scottish Church when a youth and an exile in that country. On recovering the throne of his ancestors he naturally desired that his people should be brought to the knowledge of the Savior. At his request the elders of Iona sent him a missionary band, headed by the pious and faithful Aidan. The king assigned them the island of Lindisfarne for their residence. Here Aidan established the system of Iona; and the community lived according to monastic rule. Numbers gathered to the new monastery both from Scotland and Ireland. The king himself zealously assisted in spreading the gospel: sometimes in preaching, and sometimes acting as an interpreter, having learned Celtic during his exile. Bede, though strongly Roman in his affections, bears hearty testimony to the virtues of these Northern clergy—"Their zeal, their gentleness, their humility and simplicity, their earnest study of scripture, their freedom from all selfishness and avarice, their honest boldness in dealing with the great, their tenderness and charity towards the poor, their strict and self-denying life."
The work of conversion appears to have prospered in the hands of both Augustine and Aidan. The Italian monks extended their teaching and influence over the south and south-west of the kingdom, while the Scottish monks spread the truth of a clearer and simpler gospel over the northern, eastern, and midland provinces. At one time the sees of York, Durham, Lichfield and London, were filled by Scotchmen. Thus Rome and Iona met on English ground, a collision was inevitable; who would be master? Augustine, who had been consecrated primate of England by the pope, required the Celtic monks to conform to the Roman discipline: this they steadfastly refused to do, and defended with great firmness their own discipline and the rules of Iona. Serious disputes now arose. Rome could submit to no rival; she was determined to hold England in her grasp.
After the death of the pious and generous Oswald, the throne was filled by his brother Oswy, who also had been converted to Christianity and baptized in Scotland during his captivity. But his princess adhered to the customs of Rome, and the family followed the mother. A strong influence was thus brought to bear against the Scottish monks; and wearied with the continual taunts and the unscrupulous conduct of the pontiff's agents, both sacred and secular, the unyielding presbyters determined to leave England and return to Iona. By far the largest and most important part of the country had been converted to Christianity by means of their labors; but the triumph of Rome at the Whitby conference in 664, through the subtlety of the priest Wilfred, so discouraged them that they quietly withdrew from the field after occupation of about thirty years. "However holy thy Columba may have been," said the crafty Wilfred, "wilt thou prefer him to the prince of the apostles, to whom Christ said, Thou art Peter, and I will give unto thee the keys of the kingdom of heaven?" King Oswy was present, and professed obedience to St. Peter, Lest, he said, when I appear at the gate of heaven, there should be no one to open it to me. The people soon followed their prince, and in a short time all England became subservient to Rome. But neither arguments, intimidation, nor derision, had any effect on the presbyters of the North. They refused to acknowledge that they owed any allegiance to the bishop of Rome. Scotland was still free. How to enslave her was now the great question with the Romanists. The priests, as usual, set to work with the princes. It was accomplished in this way: -