Last Christmas what is the song about?

Just what the song implies. I learned this one back in Bergen School. Christmas is coming, O the Happy Day, Christmas is coming, sing a rondelay ( a type of song or dance, evidentally) Through the air gay tunes are ringing, can it be the Angels Singing, on this Happy Day. There is a similar second verse that ends- Christmas is here. I have heard the song was of Polish origin.