The word hymn comes from the Middle English word imne, Old French ymne, Latin hymnus and Greek humnos. Webster's Revised Unabridged Dictionary describes it as a song of praise to God, to a saint or to a nation, although in reality many hymns are just poems set to music about ourselves. (Schoolboy joke: Why do we say 'hymn' and not 'her'? Because we say A-men1 and not A-women!)
Of old, hymns were mainly the chanting of a Psalm, whereas today the definition is more loose and can take the form of a Christmas carol, Gospel song, anthem, etc., or even a folk song.
Singing makes us feel good and that's why we sing; whether it's a hymn, pop song, rap, opera, or whatever turns us on. Singing helps us feel young and energetic, even if we're not very proficient. Singing helps relieve tension. (Tip: If you think you might start crying and feel embarrassed at a wedding or funeral, make sure you join in that opening hymn. Singing with an appropriate amount of gusto really is therapeutic!)
The congregation at a Christmas Carol service, or guests at a wedding, are not an audience; communal hymn singing makes people participants. Communal hymn singing is a concerted exercise that helps everybody get in tune with each other; mentally and spiritually, if not musically.
Weddings in Japan
At a western style wedding in Japan the hymn usually sung at the start is quite an interesting choice for a wedding, and probably chosen for the familiar melody rather than the words. The hymn is:
Christmas in Japan
Japanese enjoy Christmas carols as much as the rest of the world, even though only a tiny percentage of Japanese are Christian. They enjoy the old favourites, such as: