Complex sentence: Agantyr did permit 30 young men to return to Frisia with Willibrord with the intent to educate them and perhaps convince some of them to join his efforts to bring Christianity to the savage Danes.
Split into simpler sentences: Agantyr did permit 30 young men to return to Frisia with Willibrord. Perhaps Willibrord's intent was to educate them and recruit some of them to join his efforts to bring Christianity to the savage Danes.