Beethoven’s pianoforte variations bearwitness to an important characteristic of his entire creative output: the principle of presenting a musical idea in ever new alterations.
[This principle] is linked perhaps in the first place with the prevailing intellectual approach to the material that is characteristic of Beethoven and all the Classicists as opposed to the preponderance of free inspiration in the works of the Romanticists.
In the second place, however, this principle was rooted in the essential trend of Beethoven’s mind, in his instinctive inclinations, so that it manifested itself not only in the variation form but, in “continuous” variations of often the smallest motif, remained significant up to the very last works of the Master. (From the preface)