On Wednesday, many Christians will show up to work with ashes smudged on their foreheads. Many more will head to church on their lunch break or after work to receive a cross of ashes on their face.

This year, Ash Wednesday — a solemn day of fasting and reflection to mark the start of Christianity’s most penitent season — on March 5.

But what exactly is the purpose of the centuries-old Christian tradition?

In the Christian tradition, Ash Wednesday marks the start of the holy season of Lent, a time for reflection and repentance in preparation for the celebration of Easter.

Christians from many denominations recognize the holy season for 40 days leading up to Easter. For centuries, Christians have received a sign of the cross with ashes on their forehead at the beginning of that season as a reminder of mortal failings and an invitation to receive God’s forgiveness. The tradition has its origins in the Old Testament where sinners performed acts of public penance.

The use of ashes is to remind parishioners of their mortality. During Ash Wednesday service, the phrase, “Remember, man, that you are dust and to dust you shall return,” from the Book of Genesis is traditionally employed.

Rev. Gregory Wilson, pastor at St. Mary’s Help of Christians Catholic church in Aiken, South Carolina, offers believers two things to consider when observing Ash Wednesday: prayer and sacrifice.

“Prayer,” Wilson said, “purifies intentions and relates everything back to God. Fasting detaches people from comfort and themselves, in turn, making them ‘hungry for God’ and his righteousness and holiness.”

Wilson urges Christians to make time for prayer, nothing that “people always have time for what they want to do.”

“We make time for these things because they are a priority and they are necessary in life and guess what? So is prayer. Prayer is like the air for the lungs of the Christian. So do not try to find time – make it.”

Ash Wednesday is not a fixed date. Its timing is tied to Easter Sunday, and for most Christians, Easter will fall on April 20 this year.

Easter also moves annually, swinging between March 22 and April 25 based on a calendar calculation involving the moon.

This year, Ash Wednesday will fall on March 5.

Typically, the ashes are from the palms used on Palm Sunday, which falls a week before Easter, according to the Evangelical Lutheran Church in America.

Ashes can be purchased, but some churches make their own by burning the palms from prior years. For example, several parishes and schools in the Chicago Catholic Archdiocese plan to hold palm burning ceremonies this year.

Lent is the annual period of Christian observance that precedes Easter. The dates of Lent are defined by the date of Easter, which is a moveable feast, meaning that it falls on a different date each year. Lent starts on Ash Wednesday, and its observance lasts for 40 days, excluding Sundays.

Catholics started the tradition of Lent around the year 325, during the Council of Nicea, but it has spread through other Christian denominations, including Western Orthodox churches, Lutherans, Methodists, Presbyterians and Anglicans, among others.

During lent, Christians give up things like habits or food and drink items. The tradition’s origins go back to Jesus’ 40 days of temptation in the desert.

Lent comes from the Middle English word “lente,” which means springtime, and signals the coming of spring.

On the Tuesday before Ash Wednesday, people tend to eat rich foods in large quantities in advance of the fasting, which is a key component of Lent. Hence, the name “Fat Tuesday.”

The Associated Press contributed to this story.