Reformed congregations are adopting Lent for the very same reason. People like Lent. It is socially acceptable, even hip to go about with ashes on one’s forehead once a year. It seems counter-cultural but when the cultural approves of it, beware. The culture is not so “chill” with Christ’s cross and the foolishness of the gospel but they approve of Lent because it looks like something they can understand: works (στοιχεῖα).
In the Western church calendar Lent began yesterday on “Ash Wednesday.” Lent did not exist in any form in church law until 325 where the word appears in Canon 5 of the canons of Nicea. Even then there is no detailed prescription in the canon itself. The 4th century was, in many ways, transformative for the theology, piety, and practice of the church and not always for her benefit. We know that very early on there was deep concern (e.g., the Quartodeciman controversy) over the correct time to observe Easter but beyond that the church calendar was sparse. By the time of the Reformation, however, the church calendar (or the liturgical year) became so extensive that there was something to be observed (e,g., feast days) virtually every day of the year. The origins of Ash Wednesday itself can be no earlier than the early medieval period. Once Lent entered Christian practice, it began on a Sunday. It was only moved to what became “Ash Wednesday” “later” (so the Oxford Dictionary of the Christian Church) in order to bring the observance to 40 days (in imitation of Christ’s 40 days in the wilderness, no doubt). There is nothing of Ash Wednesday or Lent in the earliest post-apostolic Christian theology, piety, or practice. The date for Easter was controversial was because both sides were arguing over which date was more biblical. No one was arguing in the early 2nd century that the church has authority to impose practices and observances that are not imposed in Scripture.
In other words, the very practice of Ash Wednesday and Lent are simply made up observances and this is the problem. It is not that one might not learn something valuable by abstaining from this or that for 40 days or that there is no value in gathering on Wednesday 40 days before Easter to remember the suffering and death of our Savior. The problem is that the human heart is an idol factory (Calvin). Once it is given license to create and impose Christian observances, it never ends. What begins with good intentions becomes a form of bondage. This is not a new problem. The Apostle Paul opposed this very thing in his epistle to the Colossians:
If you have died with Christ to the elementary principles (στοιχεῖα) of the world, why, as if you were living in the world, do you submit yourself to decrees, such as, “Do not handle, do not taste, do not touch!” (which all refer to things destined to perish with use)—in accordance with the commandments and teachings of men? These are matters which have, to be sure, the appearance of wisdom in a self-made religion (ἐθελοθρησκίᾳ) and self-abasement and severe treatment of the body, but are of no value against fleshly indulgence (Col 2:20–23; NASB95).
In the case of Ash Wednesday and Lent we have the very thing against which the Apostle Paul warned: “will worship” (ἐθελοθρησκίᾳ). Christians have added and imposed upon other Christians the very sort of abstinence and man-made religious practice condemned by the Apostle. The elementary principles (στοιχεῖα) to which Paul refers are not observations about nature (as some commentators think) but rather he is most likely referring to the fundamental principle of law. Someone was seeking to put the Colossians back under the law of abstinence as a mark of piety and Paul was not having it. This is typically the Lutheran explanation of the passage so it is striking to see leading (even confessional) Lutherans doing what their own tradition tells them they ought not.
It is even more striking to see NAPARC churches adopting Lent. The Directory for Publick Worship denounces observance of Lent and the medieval practices. It is striking because sola Scriptura was the formal cause of the Reformation.