Sunday Express Skeleton 24Th November...
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No best answer has yet been selected by timserving. Once a best answer has been selected, it will be shown here.
For more on marking an answer as the "Best Answer", please visit our FAQ.I believe its origin is religious. There is a hymn "Fight the good fight with all thy might - God is thy strength and God thy right..." The theme throughout is that however tough things might be, you'll get through because God is on your side.
I assume it means to fight for what is seen to be right in the eyes of God.
There are popular stories about brides-to-be coming in to church to the accompaniment of "See the Conquering Hero Comes" and going out to "Fight the Good Fight" but how much truth there is in them, I couldn't be sure...