Ash Wednesday is the first day of the six weeks prior to Easter Sunday that mainly Roman Catholics, but some Protestant denominations celebrate annually by drawing a cross on their foreheads with ashes. As it is the first day of Lent, it begins a season of fasting and penitence generally as a means to try to gain favor with God. While the intentions of Ash Wednesday observers may seem good, the bible never mentions the day — or Lent for that matter — and actually explicitly prohibits some of the ritualistic behavior of Ash Wednesday.
See also: Five Reasons Not to Observe Lent
As stated, the purpose of Ash Wednesday is to kick off the first day of Lent by painting a cross of ashes on one’s forehead. This practice contradicts the biblical design for fasting, which states,
And when you fast, do not look gloomy like the hypocrites, for they disfigure their faces that their fasting may be seen by others. Truly, I say to you, they have received their reward. But when you fast, anoint your head and wash your face, that your fasting may not be seen by others but by your Father who is in secret. And your Father who sees in secret will reward you.Matthew 6:16-18 (ESV)
The point is, fasting is not to be a public or corporate action. It is to be private and kept between you and God. The public spectacle made out of the Roman Catholic and mainstream observance of Ash Wednesday is an affront to the Scriptures, and Jesus said that the attention they receive on Earth is their reward.
It was common for the Pharisees to practice their righteousness before men because they were not regenerate, true believers in Jesus. They were, in fact, self-righteous and their strict observance to the law was not to honor God but to make themselves look righteous before men. This is the same practice we see in the throughout the Roman Catholic Church — not just with Ash Wednesday, but with the entire practice of works righteousness. The idea is to try to earn favor with God by practicing your righteousness before men while, in reality, you have no real love for the God who has revealed himself to us.
It is important to remember that while the Scriptures don’t strictly prohibit the observance of special days — even when their not explicitly mentioned in Scripture — that many of the ritualistic practices in some of these extra-biblical holidays are forbidden and should be avoided. Further, it is important to remember that no amount of ritual or special day observance is going to earn you favor with God.