I think there are two meanings here, the obvious one on top about vikings literally fighting to protect Asgaard, and underneath the struggle of the modern Ãsatrúar against other religions. This is especially clear if you look at their other songs. The three giants would be Judaism, Christianity, and Islam, three religions that control the world that originated south of Scandinavia. Their history shows that they lied to destroy pagan religions and still do to this day. So to use some quotes from the song, modern Ãsatrúar are trying preserve their religion against these three "giants" and their "lies", making them "the guardians of Asgaard".
I think there are two meanings here, the obvious one on top about vikings literally fighting to protect Asgaard, and underneath the struggle of the modern Ãsatrúar against other religions. This is especially clear if you look at their other songs. The three giants would be Judaism, Christianity, and Islam, three religions that control the world that originated south of Scandinavia. Their history shows that they lied to destroy pagan religions and still do to this day. So to use some quotes from the song, modern Ãsatrúar are trying preserve their religion against these three "giants" and their "lies", making them "the guardians of Asgaard".