Does fasting the Day of Ashura expiate the sins of the past year, and does that include major sins? What is the reason for venerating this day?

Fasting the day of Ashura expiates the sins of the previous year. The Prophet, peace and blessings be upon him, was keen to fast it due to its special status and virtue. The reason he fasted it, peace and blessings be upon him, was that the Jews used to fast it in gratitude to Allah for saving Moses and his people from Pharaoh. So he, peace and blessings be upon him, said: «I am more worthy of Moses than you.» Thus, he fasted it and commanded its fasting. The expiation achieved by fasting Ashura only covers minor sins. As for major sins, they require specific repentance.