For more on the occult meanings of calendar days see Occult Meanings of Winter Solstice and Christmas | AstroTheology.
Source - Hoaxes
In 1708 a correspondent wrote to the British Apollo magazine asking, "Whence proceeds the custom of making April Fools?" The question is one that many people are still asking today.
The puzzle that April Fool's Day presents to cultural historians is that it was only during the eighteenth century that detailed references to it (and curiosity about it) began to appear. But at that time, the custom was already well established throughout northern Europe and was regarded as being of great antiquity. How had the tradition been adopted by so many different European cultures without provoking more comments in the written record?
References to April Fool's Day can be found as early as the 1500s. However, these early references were infrequent and tended to be vague and ambiguous. Shakespeare, writing in the late sixteenth and early seventeenth centuries, made no mention of April Fool's Day, despite being, as Charles Dickens Jr. put it, a writer who "delights in fools in general."