Hard-line followers of Dumezil’s three functions theory (and there are still a few out there) will find this contradictory, since the Vanir are placed in the third function (fertility) and not the second, which is the warrior’s. Yet one brief look at a few other mythological examples should be enough to, at the very least, question the use of Dumezil’s theory: Demeter is mentioned as a law-giving goddess, Thor and Jupiter have fertility-related aspects (bringers of rain, anyone?), Frey is placed as a divine ancestor of a Swedish royal dynasty. The three functions theory may be useful to trace back the origins of religious systems, but that’s it. A tree may come from a seed, but it is not a seed; modern-day mammals may descend from pre-historic rodents, but we are not rats; Indo-European cultures may be traced back to a common origin, but they are not limited to it. Things change, evolve, diversify – they are more than their origins! And while some may not adhere to Dumezil’s ideas, they may nonetheless expect gods to be neatly organized with a clear-cut separation of functions and no overlapping. Which is also far from the truth, as the aforementioned examples and others show.
Perhaps a good way of understanding Frey’s bellic side is by looking at other deities who are unexpectedly connected to war. Take Juno, for instance: She’s mostly a goddess of women, childbirth and the moon, yet in ancient Rome She also had a military aspect under the name of Juno Curitis. The title may derived from curiae, the military and administrative units of Rome, or the Sabine word curis, which means spear. An Italian prayer to Her mentions Juno’s chariot and shield and She had a temple in the Field Mars, in what is yet another military link.
It is interesting to notice that Juno is not associated with war per se, but She apparently presided over a territorial unit that also served as a tool to organize military forces. As such, the recruited men would have Her as a patron of sorts, the goddess of their curia and would count on Her when fighting on the battlefield. A similar aspect is that of Juno Populona, from populus, a word that came to mean people, though it may have originally meant infantry. This aspect of Her goes back to the pre-Republican period, eighth to sixth centuries BCE, a time when there was little or no professional army. The “people” would therefore create an ad hoc force of armed citizens under the protection of Juno. Again, not a war deity per se, but one that rises and fights when and if necessary. Which is how I see Ingui-Frey’s military aspect.
He’s not a god of the professional soldier, of those who join or even seek the battlefield as a way of life, but of “armed citizens” or farmers. Those who fight for a living don’t work the fields or try to solve matters in a parliamentary war of words. In fact, in the old days a full-time warrior was the exact opposite: he looted for a living and scorned too much talk and not enough action; to some extent, this is still true today. Frey’s host is somewhat like Juno Populona’s, people whose primary occupation is not war and would frankly prefer to live without it. But when war does come and there’s no way around, they stand up and fight. They fight to protect their crops, animals and family, they fight for the preservation of the bonds that keep their community together. They’re the common folk that takes up arms or Robin Hood’s merry men, the lambs that rise to become lions (or rather boars) before returning to their lives as lambs. They don’t live for war and would gladly avoid it, but they will fight as a last resort, boldly and to the best of their abilities.