"Vom Himmel hoch, da komm ich her,
ich bring euch gute neue Mär;
der guten Mär bring ich so viel,
davon ich singen und sagen will."
(Martin Luther, 1535)
This anonymously handed down chorale arrangement is reminiscent of Bach's early style with technically solid voice leading and typical ascending and descending scales, which Bach also used in his other organ works on this Christmas tune.
On the other hand, we find some chord passages in the mainly three-voiced piece (even including parallels), which are rather giving us some doubt about Bach's authorship.
This edition should not be seen as an effort to improve the original score, but just as a suggestion of a variant as a straight chorale trio.
If you are interested in my version, feel free to download the score - look here for an earlier version and the pdf:
https://www.contrebombarde.com/concerthall/music/36228