Song sung by children in school

I really like how when Abby is at the school she walks by a classroom and children are singing "The Battle Hymn of the Republic" which if I recall my history correctly was a marching song of the North's army during the United States' Civil War. The song is partly about the return of Jesus Christ to the earth to reward the righteous and punish evil doers which is exactly what is happening in the movie. And Jesus is this mysterious "David" for whom she is land lady.