Raga of Hindi songs

[Oldposts]

Hi everybody. My name is Rajen Mohunlal and I'm from South Africa.I enjoy bhajans and kirtans tremendously, and also film songs to a small degree. I have two questions :- 1). What is the difference between a bhajan and a kirtan, and 2). If a person can sing a song, then why is it so neccessary to know what raag the song is ung in - how does this help?.This may sound a strange question to those who have studied music, but I have not studied and am therefore puzzled.