There are many myths and stories about why we celebrate Holi, but the most famous one is about an arrogant but powerful demon king Hiranyakshipu. His son Prahlad was devoted to Lord Visnu and refused to worship his demonic father. Hiranyakshipu did many things to try to kill Prahlad, but he managed to survive all attempts. The final attempt was when his aunt Holika attempted to burn him (she was immune to fire), but as all good tales end, Prahlad was saved through divine intervention while Holika and Hiranyakshipu died. This is how the 9th incarnation of Visnu was born as Narasimha (half man half lion). As with many of the festivals in India, the theme is the triumph of good over evil and the destruction of demons either external or within ourselves. On the day of Holi people build bonfires symbolizing the destruction of evil. The 8 days prior to Holi are considered inauspicious for starting or buying anything new.
This year is very interesting because Holi falls on the total lunar eclipse. I happened to be in India the last 2 years for Holi and feel connected to the story of Prahald in my own life situation. Without going into details it feels like I am Prahlad.