Ash Wednesday-Holy Week
The first Christians observed with great devotion the days of our Lord's passion and resurrection, and it became the custom of the Church to prepare for them by a season of penitence and fasting. This season of Lent provided a time in which converts to the faith were prepared for Holy Baptism. It was also a time when those who, because of notorious sins, had been separated from the body of the faithful were reconciled by penitence and forgiveness, and restored to the fellowship of the Church.
Thereby, the whole congregation was put in mind of the message of pardon and absolution set forth in the Gospel of our Savior, and of the need which all Christians continually have to renew their repentance and faith.
-Book of Common Prayer
Ashes are an ancient sign of penitence; from the middle ages it became the custom to begin Lent by being marked in ash with the sign of the
cross. For the duration of the Lent season, liturgical dress is the simplest possible. Churches are kept bare of flowers and decoration and Gloria in Excelsis is not used. This is to reflect the solemnness of the season.
-Times and Seasons, The Church of England