For the Christian Celts, the Monday (and sometimes Tuesday and Wednesday) of Holy Week was dedicated to cleaning the house and the home (with Holy Thursday dedicated for cleaning the chapel).
After months of inside smoke from the hearth dusting everything with soot, and with the spots above and around the well-used candles getting dingy and oily, Spring cleaning served both practical and spiritual purposes. Spring was a time of renewal, and so it made sense to renew the home from the dinge of winter.
But, as importantly, Spring cleaning mirrored the inward housecleaning of the Lenten days. With Easter almost upon them. the last few corners of the soul were tended, swept, and exposed to the light for purification.
Reluctant Xtian 
I love these articles about your Celtic heritage practices! I actually bought some Rowan tree twigs and berries to hang above our door after reading your article on the Rowan tree last year. Thank you for these writings.
Glad it’s interesting and helpful!