Why Sunday is a general Holiday?
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There are many beliefs regarding Sunday as Holiday. According to Christianity, God created the world in 6 days, and no 7th day he took rest, therefore it's declared a holiday. Also, it's the day of christ's Resurrection, hence it's the day to worship God.
Sunday as the holiday was first introduced by the British government in 1844 for the school students because they wanted to engage school students in some creative activities to discover their passion other than academics. But for people like me, it's the day to sleep and only sleep.