Catholic Mariology can be a contentious subject. The most serious criticism that is made of Catholic Marian piety — for example, praying traditional Marian prayers such as the ‘Hail Mary’ and ‘Hail Holy Queen’, including statues and icons of Mary for use in churches and shrines, etc. — is that it is a form of idolatry.
It’s important to note first of all that idolatry is considered a very serious “mortal” sin in Catholicism. Committing a mortal sin and dying in the spiritually derelict state caused by serious sin is how Catholics believe one goes to Hell. Therefore, Catholics should take the charge of idolatry very seriously.
Is Marian devotion a form of idolatry? At first glance, it would seem that it may not be. Whom else do we keep pictures of? Our friends, family, and loved ones. If we keep pictures of such people, why not keep memorials to the Virgin Mother of God, a Saint of a particularly legendary caliber? In Luke’s Gospel account, the holy angel Gabriel, who spends his days in the presence of God, calls her “blessed among women”. Shall we keep memorials to our grandparents, friends, and relatives, but none to Holy Mary, the one that angels call blessed?
Anecdotal defense can only go so far, however. A more robust defense of Catholic Mariology could be made by carefully describing what it would take for Marian piety to be idolatry. This line would take the form of a negative defense — it would show what would be idolatry, so as to test whether or not the Catholic faith is innocent or guilty of it.
First, and most centrally, idolatry is giving to another the worship due to God alone. If a Catholic ascribed to Mary the glory due God alone, that would be idolatrous.
Traditionally, Catholicism draws a distinction between two forms of honor or glory that is attributed to persons. First there is “latria”. Latria is often translated “adoration”. In the Nicene Creed it is written that the Holy Spirit is “adored and glorified” with the divine persons of the Father and the Son. Adoration is the worship that is due God alone. To “adore” Mary in this sense would be to commit the grave sin of idolatry.
The second form of religious honor or piety that Catholicism upholds is “dulia”. Dulia is a form of piety, but it is not “worship” in the sense that adoration is worship. Dulia may include prayer. Catholics do not believe that giving dulia to someone known to be in Heaven is a form of idolatry. Interestingly, John Calvin denied that there is a distinction between latria and dulia. Ultimately, a sufficient rejection of Catholic Mariology must successfully argue that between latria and dulia there is no difference.
Traditionally speaking, however, Catholics pray to Mary and accord her “hyperdulia”, though not latria. Whatever power she has is due to the grace of God. Therefore, she is not honored in the way that God is. And yet, as the Scriptures prophesy, “Blessed art thou among women”.