Apologies if I have grossly misunderstood the common image of the violent, merciless barbarian that is attributed to the late antiquity Germanic tribes like goths and vandals (as well as the later norse), but it seems like the image of a "weak" peaceful figure in Jesus would be less attractive to such a society than Thor or the Germanic pantheon. Why did a warrior culture eschew warrior gods for that of a foreign carpenter that told them that the merciful were blessed and the peacemakers were the children of god?
Did missionaries present the gospels in some unconventional way, perhaps emphasizing the OT Father or portraying christ in a different way than how he was preached in the Mediterranean? I'm just interested in why such a culture would do such a 180 on the subject of its worship. A god with a hammer seems to fit my image of the barbarians at the gate, but they dropped those gods despite little outward change in the rest of their society (to my understanding).
I want to challenge your assumptions, not about the Germanic tribes, but about Jesus' public image.
The Romans were also warriors, and they converted (under an emperor who won battles when he started using the sign of the cross). What sort of Jesus do you think their missionaries would have been preaching in the North?
To really understand the Germanic and Scandinavian tribes, we have to look at their literature. In it, we see a measure of the same stoic resignation to suffering that the classical world had, upon its conversion, projected on Christ.
So it's because of his strength that these ancient societies believed Jesus was willing to submit to death -- not his love, or mercy, or something else namby-pamby like that. His strength. Notice that this reading jives better with the original gospel accounts, too: resurrection makes much more narrative sense if the person who died was stronger than death.
Looking at the gospels and the way theology has built up in the West, we have to conclude that Jesus' actions were of greater significance than his words to gentile Christians in the first millennium of the church.
One final source to look at is The Heliand , which means The Savior in Old Saxon. This was a very politically significant version of the gospels for Saxons, and depicts Jesus as the leader and his twelve disciples as a band of warrior-brothers. One passage goes:
Then he spoke and said there would come a wise king,
magnificent and mighty, to this middle-earth;
he would be of the best birth; he said
that he would be the Son of God,
he said that he would rule this world,
earth and sky, always and forevermore.
he said that on the same day on which the mother gave birth to the
Blessed One in this middle realm, in the East, he said,
there would shine forth a brilliant light in the sky, one such as we
never had before between heaven and earth nor anywhere
else, never such a baby and never such a beacon.
tl;dr -- your guess that it was about presentation is right, but they probably didn't have to change their presentation all that much.