At last, unable to endure longer the envy of his fellow pupils, Kentigern ran away. And when S. Servan discovered it, he pursued him, and reached the bank of a river, but Kentigern had escaped to the other side. Then the old man cried to him, "Alas! my dearest son, the light of my eyes, and the staff of my age, wherefore hast thou deserted me? Remember that I took thee from thy mother's womb, nursed thee, and taught thee to this day. Do not desert my white hairs."
Then Kentigern, bursting into tears, answered, "My father, it is the will of the Most High that I should go."
Servan cried out, "Return, return, dear son, and I, from being a father, will be to thee as a son, from being a master I will become a disciple."
But Kentigern, suffused with tears, replied, "It cannot be, my father; return and admonish thy disciples, and instruct them by thine example. I must go where the Lord God calls me."
Then Servan blessed him across the river, lifting up his holy hands, and sorrowfully they parted the one from the other, to see each other's face no more in this life.
Kentigern settled near Glasgow, where he inhabited a cave in the face of a rock, where the people looked at him with respectful curiosity, while he studied the direction of the storms at sea, and drank in with pleasure the first breezes of the spring. Having converted many of the people, together with the King of Strathclyde, he was consecrated Bishop by an Irish prelate, the Keltic Church being ignorant of the Nicene canon requiring three to consecrate, "with unction of holy oil, invocation of the Holy Spirit, and imposition of hands."
The district of Strathclyde, or Cumbria, on the west coast of Britain, from the mouth of the Clyde to that of the Mersey, that is to say, from Glasgow to Liverpool, was occupied by a mingled race of Britons and Scots, whose capital was Al-Cluid, now Dumbarton. It was in this region that S. Kentigern was called to labour.
As bishop, he still dwelt in his rocky cell, where he used a stone for a pillow, and to inure his body to hardships, he stood in the Clyde to recite his psalter. He wore a dress of goat-skin bound about his loins, and a hood, and over all, his white linen alb, which he never left off; and carried in his hand his pastoral staff of wood without ornament, and in his other hand his office book. Thus he was ever prepared to execute his ministry; and thus attired, he went through the kingdom from the Clyde to the Firth of Forth. In his cell he lived on bread and cheese and milk, but when he was with the King, he relaxed the severity of his fasting, so as not to appear ungracious when offered more abundant and better food; however, on his return to his cell, he curtailed his allowance, so as to make up for his relaxation of rule at court.
When S. Kentigern was made Bishop of Glasgow, Gurthmel Wledio was King of the North Britons. He was succeeded by Roderick the Liberal (Rydderach Hael), a religious and deserving prince, who was driven by his rebellious subjects under Morken Mawr to Ireland. Morken having usurped the throne of Strathclyde, drove S. Kentigern out of the country, and the Saint took refuge in Wales with S. David, Bishop of Menevia, and remained with him till the Prince of Denbigh bestowed on him lands, where he built the famous monastery of Llan-Elwyn, afterwards called S. Asaph. Here he gathered about him a great number of disciples and scholars, and he was there at the date of the death of S. David, in 544.
On the death of Morken, Roderick returned to Scotland, and recovered his crown. He immediately recalled Kentigern to his see, and he, leaving his monastery to the care of S. Asaph, went back to Glasgow in 560.