Scholars do not converge on when this chorale prelude was written. Nobody really knows if it is an early work or rather a late one. The issue is far from being solved.
It seems the chorale tune is based on a rhenish folksong, which appeared in 1599 in the “Alte Katholische Kirchengesang”. What we know for sure is that the composer was familiar to such a song, for the “Singverein” used to include Praetorius 1609 version in some of its concerts, by the time Brahms was living in Wien.
Regarding the use (or not) of the pedalboard, the conclusion is that Johannes could have played “some of the bas notes, particularly the tonic half-notes that appear at cadential points, on the pedal.” (Ap. OWEN, B., “The Organ Music of Johannes Brahms”, p. 104, ed. Oxford University Press – 2007).
Worldwide cherished this homophonic composition is known as “the most happily inspired and original of Brahms’s chorale settings for organ”. (Ap. JORDAHL, R. A., in “A Study of the Use of the Chorale in the Woeks of Mendelssohn, Brahms and Reger”. – Ph. D. dissertation – University of Rochester, 1965, p. 381).
It is clear that Brahms meant a registration differing especially in colour, rather than in dynamics.. As a matter of fact, that is the conclusion to which one arrives based on two linked facts: First, he does indicate changing of manual along the staves, and: Second, there is but one, and no more than one, dynamic mark, at the very beginning of the chorale: “piano dolce”.
Unlike “Herzliebster Jesu” (#2 –actually #3 in the original manuscript), there is no crescendo indication whatsoever.