The heir to the Bernician royal line was Oswald, younger brother of Eanfrith and one of the many sons of Aethelfrith. He had been in exile in the west of Scotland and Ireland, under the protection of the Irish lords of Dal Riada. During his exile, Oswald became a Christian, schooled in the Celtic brand of Christianity of the monks of Iona. Assisted by troops from the Irish king, he gathered his forces and marched to meet the British king Cadwalla. Bede gleefully paints a picture of the devout Christian king, describing how the night before the battle, Oswald had a vision of Saint Columba, who told him "Be strong and act manfully. Behold, I will be with thee. This coming night go out from your camp into battle, for the Lord has granted me that at this time your foes shall be put to flight and Cadwalla your enemy shall be delivered into your hands and you shall return victorious after battle and reign happily." Oswald recounted the vision to his war council and it was agreed that if they survived the battle they would all be baptised into the Christian faith.
Oswald ordered a wooden cross to be erected, and he held it in place as his men fastened it into the earth. He then knelt in prayer and asked his army to pray with him. When the battle was joined, Oswald faced far superior numbers, but his band of loyal followers, feeling God was on their side, routed the British enemy and their king, Cadwallon perished in the fighting. Bede's use of Oswald as an exemplar of Christian superiority somewhat colours the narrative of Oswald's achievements, but it is clear that he became a renowned and beloved leader to his followers, and he was formidable in battle. Following his victory, Oswald established himself as ruler of a united Northumbria. He was recognised as Bretwalda and according to Bede's account, he "brought under his dominion all the nations and provinces of Britain".
Oswald sent for monks from Iona to set about the conversion of his people. The first priest was not well received but when his replacement Aidan arrived from Iona, his gentle approach endeared him to the Northumbrians. Oswald granted him the island of Lindisfarne to build his monastery, which flourished, particularly in the latter years of the 7th century and throughout the 8th century, which saw the production of the Lindisfarne Gospels.
The success of Aidan's ministry was due perhaps in no small part to the fact that Oswald himself acted as interpreter, having learned Gaelic in exile. He translated the monk's native Irish preaching for his Northumbrian court. Oswald is noted for his piety and good deeds in life, and Bede recounts several acts of kindness that particularly stood out. Among them is the tale of the blessing of his arm by Aidan after Oswald broke up silver platters from his feast to be distributed to the poor at his door.
The Mercian Saxons had been somewhat held in check by Oswald's defeat of their British allies under Cadwalla when Oswald came to power, but by the 640s AD, their king, Penda, who had previously defeated Edwin, had resumed his military ambitions and he began a campaign against the Northumbrians, gathering allies from the Welsh kingdoms of Powys and Gwynedd. Penda's machinations culminated in the battle of Maserfelth which may have been in the midlands in Shropshire, in the territories bordering the two realms. Oswald's army was defeated and he was slain on the 5th of August 642 AD aged 38.
His body was ritually dismembered and left on the battlefield with his limbs and head placed on poles and his torso tied to a tree in mock crucifixion. Before he was killed Oswald knelt and prayed. Bede records, " …his life closed in prayer; for when he saw the enemy forces surrounding him and knew that his end was near, he prayed for the souls of his soldiers. 'God have mercy on their souls, said Oswald as he fell' is now a proverb…the king who slew him ordered that his head and hands with the forearms be hacked off and fixed on stakes." Oswald's last words have also been interpreted as asking for forgiveness of his murderers, an ultimate expression of the Christian ideal of turning the other cheek.
Following his death, Oswald's dismembered body was eventually rescued and distributed as relics. According to Bede, "when Oswald was killed in battle, his hand and arm were severed from his body, and they remain uncorrupted to this day. They are preserved and venerated in a silver casket at the church of Saint Peter in the royal city, which is called after a former queen named Bebba." Which is to say, that Oswald's arm was venerated as a relic in the 8th century church in the fortress of Bamburgh during Bede's lifetime.
Bede's use of Oswald as a Christian martyr gives us an insight into the world of the Anglo-Saxons. At this time, books were incredibly valuable and rare, so for the new Christian movement to flourish preaching and oral storytelling were vital. The Christians had to demonstrate the advantages and power of their religion, and stories that demonstrated the efficacy of their faith and which legitimised it in terms of the endorsement of the ruling classes were important in strengthening the faith of new converts and encouraging non Christians to accept the faith.
Oswald was an ideal figurehead as his pious conviction and commitment to Christian beliefs was a hallmark of his reign. His political power and popularity could be equated with his faith, so by bolstering his holiness with tales of miracles, the Christians were able to create him as a Christian Hero, every bit as powerful as the heroes of sagas that were the familiar ideology of traditional Saxon heritage. The famous author and scholar of Old English, J.R.R Tolkien, speculated on the existence of an epic poem centred around Oswald, and though such a poem has not survived, the idea that it could have existed clearly shows the power of the Oswald story as his cult grew after his death. Members of the Northumbrian royalty and their retainers began to take positions of authority within the church. One of the most famous is Hilda, a distant niece of Edwin. Bishop Aidan installed her as the second Abbess of Hartlepool Abbey, where she instigated a fervent remodelling of the original site, creating a beacon of Christian worship with her new buildings. In 657 AD she founded a new Abbey at Whitby, which became the site of burial for the Christian kings of Bamburgh.