From a talk to the University of the Third Age on Baroque music

Mozart was a great admirer of Handel.  Mozart’s reason for arranging of Handel’s Messiah was not because he thought he could improve on Mozart, but because, 50 years later, Handel’s music was out of fashion and Mozart was attempting to arrange it to make it accessible to the public of the day.

In the Handel original thmuivall top and bottom with hardly any inner parts – just some filling in with the harpsichord. Now, Handel was perfectly capable of writing inner parts if he wanted to – and clearly left them almost absent for a reason. But the audiences in Mozart’s day would have found the music strange and generally not to their liking.

In Mozart’s version there are three main additions.

1. Much stronger inner parts.   (Musically this is the most important change.)

2. The addition of many wind instruments.

3. It is translated into German.

There is also one subtraction – there is no organ part.

The third addition is generally beneficial because the words fit the music better.  You may think this a strange statement since it was written English.  The explanation is that Handel had in fact borrowed from himself a great deal in writing the Messiah (as well as from Wilhelm Keiser – but without acknowledgment as was his wont) and the original music was in German.  A clear example is in “For unto us a child is born”.  The strong music accent on ‘For’ is on the wrong word.

As well as fitting the words better, the sound itself – the timbre – is different because of the German rather than English language.  Again, because the songs were mainly originally in German, this is likely to be beneficial.

Of course, to assess the effect of the translation into German, we should really compare the original Handel, sung in English and in German.  But I don’t have a recording or this,  

One highly detrimental thing (but not Mozart’s fault) in the Mozart arrangement is that by his day the skill of playing the Baroque trumpet had been lost.  And hence in the famous aria “The Trumpet Shall Sound” the singer is answered not by a trumpet but by a French horn.  After several unsuccessful attempts, Mozart allocated the part to that instrument.  If you know the original it sounds incongruous, dare I say almost ridiculous. The more so because you can hear an (ordinary) trumpet in the orchestra very clearly and are reminded that that is the sound that you should be hearing. However, if you had not heard the original, or can successfully put it out of your mind, andignorreheincongruity, I think Mozart’s sounds reasonably well here.

Now, thanks to the work of Christopher Steele-Perkins, the skill of playing the baroque trumpet has been restored.

So surely there can and there be no excuse now for using unsatisfactory unsatisfactory substitutes, which gives the correct pitch but quite the wrong timbre.