Quite some immigrants and their descendants don't get these lyrics (some of them even want a new anthem) and the average Dutch doesn't understand much of it either.... German, Spain, what the hell? Myself, I am not even sure how it all originated.
I just checked the Dutch wiki-site about it and found the following info, which might be interesting.
Like many anthems, Het Wilhelmus originated in the nation's struggle to achieve independence, so that’s why it sounds patriotic.
In WWII the sixth stanza was also very popular:
A shield and my reliance,
O God, Thou ever wert.
I'll trust unto Thy guidance.
O leave me not ungirt.
That I may stay a pious
Servant of Thine for aye
And drive the plagues that try us
And tyranny away.
I really like these
English translations, meant to fit the melody, the rhyme and the acrostic.
Nowadays we are indeed not that patriotic compared to previous centuries, though this is slowly changing, due to impact of populists.
Contentwise, the Wilhelmus could be seen as sung by Willem van Oranje, dealing with a struggle. One hand he tries to be loyal to the Spanish King, on the other hand he is above all loyal to the Dutch people. It’s unknown where the lyrics come from, originally. There are different theories. One of them is that it was originally written in German, by refugees from the Low Countries, who tried to win German Fürsten for the Dutch sake.
Check here the English page if interested:
http://en.wikipedia.org/wiki/Het_Wilhelmus
From that I just copied:
"Duytsch"
There is an ongoing confusion and dispute as to what the author meant with "Duytschen bloedt" in the text, as the contemporary Dutch word "Duits" (being the modernised form of "Duytsch/Duijtsch") means "German".
Both could be correct as William of Nassau was born in Dillenburg in the county of Nassau in Germany and that it referred to William's German (rather than Dutch) descent. Others claim that it referred to the Dutch in the sense that he felt one of them rather than belonging to them ethnically. Yet another explanation is that "Duytsch" was at the time a variation of Dietsch meaning Dutch.
"Duits" is often replaced by "Diets", a cognate of "Duits", "Dutch", "Deutsch" and "Deitsch" but meaning "Dutch" rather than German. This is done mostly, or even exclusively, due to anti-German sentiment. This resentment of Germans has been present in the Low Countries since the 16th century, but today’s resentment of Germans mostly comes from the Dutch experiences in the Second World War. Hence many Dutch people after the war sung that William was of "Dutch" blood, rather than of German blood as they did not like the notion of their Father of the Fatherland being of the same heritage as the people they hated so much during the 5 year occupation. Although the exact meaning is still, and will probably remain, unclear the official version of the Dutch national anthem uses "Duits".
Cause
The last two lines of the first stanza indicate that the leader of the Dutch civil war against Spanish Empire of which they were part, had no specific quarrel with Philip II of Spain, but rather with his emissaries in the Low Countries, like Fernando Álvarez de Toledo, 3rd Duke of Alba. This may have been because at the time (late 16th century) it was uncommon to publicly doubt the Divine Right of Kings. It strikes the modern Dutch ear as an obsolete formula. For some of the resistance fighters of the day, the stanza may have resonated with irony or knowing sarcasm.
"Netherlands" and "Dutch"
The anthem refers to the "Dutch" and "the Netherlands" a couple of times. It should be noted that these words ought to be seen in context. With "Dutch people" the author meant which would today be described as "all people who speak Dutch". In William's time this included the Dutch-speakers of present-day Northern France and Belgium as well. In more or less the same way, "Netherlands" referred to the "Low Countries".