Walpurgis/Valborg was the name of the British nun (Saint Walpurga) who brought the Catholic church to Germany and was canonised on 1 May. It is exactly six months before Halloween and was a pagan celebration of spring.
Yule/Jaul Yule or Yuletide (“Yule-time”) is a winter festival that was initially celebrated by the historical Germanic people as a pagan religious festival,
There were many pagan festivities to celebrate the seasons and when the Christians came to Europe they placed their holidays at a similar time. The pagan celebrations were therefore absorbed into and equated with the Christian ones.
And as an aside
Indian summer is so called in English because the Native Americans could, if it was warm enough, grow a second crop of corn. It is called Brittsommar in Swedish because 7th October is the feast day of Birgitta.