Why do Christians celebrate Christmas Ash Wednesday Good Friday and Easter?

All of the 'holidays' mentioned above are not biblical but started by men. In particular, the largest Church - the Roman Catholic Church - incorporated each of the above into their religious calendar. After the Reformation and Anglican splits, most all 'daughter' churches continued in these celebrations. But not all Christians observe some/none of these but continue to keep the Holy Days of God first given to the Israelites and kept in the Church Jesus and the Apostles began.