Walther was more a man of learning and of writing than a flamboyant performer. In an ambience where improvisation was very much part of the organist's routine, it is remarkable to read his confession ("sub rosa"), "that though I have often have given it thought, I am unable to reach this level [of improvisation], but have to content myself with the art of composition [...]". His powers of memory too were unreliable in performance, making score reading indispensible even with his own works. With failing eyesight, his duties must have become a vexation.
Since in Walther's days most compositions circulated in handwritten copies, it was usual for a composer to copy his own and others' works. Max Seiffert has rightly praised the "accurate gracefulness" of Walther's handwriting. For a musician of Walther's stature, copying went beyond manual labour; the composer-copyist contributed his own insight and judgment. While a copy thus may be further removed from a composer's original notation, it contributes an added value as a reflection of contemporary performance practices and stylistic development. These scribal activities however were a time-consuming task that also took a physical toll. Poignant passages in his letters reveal that late in his career Walther had to scrape a living by selling his manuscript copies "at 12 pennies per full sheet, the same in parts for 6 pennies [...] but at the condition that the buyer pays the postage".
J.G. Walther, Musicalisches Lexicon (1732)
While the memory of Walther's compositions may have faded rapidly over the following generations, his activity as a scholar has been more effective in keeping his reputation alive. His Praecepta der musicalischen Composition (1708) remained unprinted. But in 1732 he published his Musicalisches Lexicon, the first encyclopedic dictionary of music to appear in the German language, containing both theoretical and biographical entries. We may be grateful that Walther actively sought to amplify his information by sending questionnaires to colleagues. Most composers represented in the Frankenberger manuscript have their entries in the Lexicon (the exceptions are Adam Nikolaus Strungk, Johann Peter Kellner and Johann Christian Scheidemantel).
 Walther: Briefe p. 60: "[...] weil ich mich nicht schäme (jedoch sub rosa) zu melden: daß diesen Punckt, ohneracht selbigem zum öfftern auch nachgedacht habe, dennoch nicht erreichen kann, sondern mich mit der Wißenschaft der Composition, und dem daher entstehenden Vermögen, etwas reelles aufzusetzen, begnügen laßen muß [...]." (6-8-1729)
 Walther, Briefe p. 135 (12-3-1731)
 M. Seiffert (see Composer and organist, n. 5), p. vi. Besides overseeing the Denkmäler Deutscher Tonkunst, Seiffert was co-editor of the Archiv für Musikwissenschaft; from 1935 till 1942 he was director of the Staatliches Institut für Deutsche Musikforschung.
 Walther: Briefe p. 224: "[...] jeden vollgeschriebenen Bogen in Partitur für 1nen guten Groschen, dergleichen in Stimmen aber ausgeschrieben für 6 Pfennige weg zu geben gesonnen bin doch so, daß der Kauffer das porto entrichte." (25-1-1740)