In Trouw, a protestant newspaper, there were arguments pro and contra for a more public exposure of the King's religion. I made a summary in English:
Your Majesty, you can not hide God
Willem-Alexander is King in the name of us all, but that does not mean he has to wipe out his own identity. The Rev. Karin van den Broeke is right: the Sovereign would do well to bear witness to his motives. Personal faith may sustain in this.
That the King is a committed Christian is beyond doubt. Take the fact that now 29 years long the King and several friends have monthly meetings to discuss faith with the Rev. Carel ter Linden (the royal family's pastor). From the accounts of the Rev. Ter Linden we know that the King is interested and actively participating during those evenings. The fact that the King did his Confirmation when he was 30 years old, shows that his choice to become a full member of the Protestant Church was well-thought and not impulsive.
In an interview with Paul Witteman (then) Prince Willem-Alexander stated that his faith "is something that leads to life." "I'm not very religious," he admitted, "but a convinced believer." Follow suit does not mean that he has to put Christianity on a pedestal. Willem-Alexander represents a country with strong Christian roots - as King he may show that.
Now the fact that the Netherlands have developed into a multicultural country, does not change this. Respect for diversity goes well with being conscious about the own history and identity. In the King's own words: "I believe that in order to function in a multicultural society, you have to nurture your own roots well."
King Willem-Alexander does not need to worry about the separation of church and state. It only requires that the state must not interfere in the policies of the church and vice-versa. The government and the Crown treat the Protestant Church like other churches: as an important but not all-powerful institution in society. The Protestant Church is not advantaged because the King accidentally happens to be a member of it.
Your Majesty, your faith is entirely private
Orthodox Protestants would like to see a pious and God-fearing leader on the throne. A figurehead of church and fatherland that propagates traditional Protestant values. Willem-Alexander can not be such a King. First, because he does not meet the profile, but also because most of the Netherlands are not at all waiting for such a sort of monarch.
By keeping a low profile about his faith, the King prevents to alienate atheïsts, Muslims, Jews and other believers. That King Willem-Alexander feels inspired by his belief in the Christian God is valuable, but it does not oblige him to demonstrate this all the time.
His mother was a bit more explicit about her faith. (Then) Queen Beatrix spoke about "a strong belief that God directs my life". The Queen went to church regularly and had frequent contact with the Rev. Ter Linden. King Willem-Alexander is completely free in forming the kingship in his own way. Invoking God in speeches is mostly tradition. His predecessors have always changed traditions and conventions. The King can do that too.
Last year the Rev. Ter Linden told in the newspaper Trouw that the young Prince Willem-Alexander was fascinated by the "stories" in the Bible. The orthodox view that the Bible contains no "stories" but "histories" did not appeal the Prince. From such a King we can hardly expect to sail a traditional religious course.
Incidentally, we should not forget that King Willem-Alexander has shown his Christian faith so now and then. During the Investiture the King mentioned that he will rule "by the grace of God." His first Address from the Throne was concluded by wishing the parliamentarians "God's blessing to rest upon them". Thus King Willem-Alexander's kingship is not thát secular.
Link to the article in Dutch:
Koning, waarom zwijgt u over God? - Christendom - TROUW
if those are the same forums that openly wish divorces and diseases on people i prefer not to read them 
