This rarely heard (and rarely recorded) work is unique in Brahms' output, and it usually said that it is the closest thing we have to a Brahms opera. It is known that Brahms throughout his life wanted to contribute to that genre, but never did because he couldn't find sufficiently inspiring texts for his tastes. So, this cantata with it's prominent part for tenor solo, which is often dramatic and recitative-like, is the closest thing we have.
Brahms wrote the bulk of it around 1863 (the final chorus was written in 1868), so it is an earlier work than it's opus number suggests, and this is evident in its style. The opening is very Beethovenian, particularly at the entry of the tenor, and some parts sound like Wagner's "Der Fliegende Höllander" (as has been noted by Malcolm McDonald), which was Brahms' favourite Wagner opera. (Despite the fractious opposition between the two camps of critics, Brahms respected Wagner's musical talent.) There are also strong echoes of the woodwind style of the Serenades, but at no point is there the effect of pastiche.

The subject of the work is the pull of duty. Rinaldo longs for his love, Armida, but must show the strength expected of a man to sail the sea and do his duty. Although such a theme seems difficult to us nowadays, it was common in Brahms' and Goethe's day (for the text is Goethe). Broadly, Rinaldo is pining for Armida (the subject of a long aria), and the male chorus is urging him to come away. He at last relents, after being shown the diamond shield, but still has thoughts for his love. Eventually his sense of duty overcomes this, and he joins the chorus to do his duty.

The work opens calmly with waving figures and brief oboe/string phrases, very appealing and aptly giving the impression of a calm sea. However, the music raises itself up for firm, dramatic chords, and the entry of the chorus confidently and optimistically, eager for adventure, with a more obvious Brahmsian style. After this long first passage, the chorus breaks off for a return to the calm opening music, which again rises to the dramatic chords. The tenor enters in the manner of a recitative (about his attachment to Armida), which eventually falls off despairingly. This leads, as one might expect, to a lengthy aria. The oboe presents its main theme with a typical Brahmsian lilt, and the tenor takes up this melody. (It is here that the music is strongly reminiscent of the Serenades.) The next phrase becomes more yearning, and then the theme is repeated with the first lines of the aria, but then continues, introducing new lines.
The tone at last becomes fuller and the music more noble and impassioned, for a while. But the choir interrupts the aria, in a warmer tone, pleading with Rinaldo, in a passage with wonderful harmonies. The tenor isn't diverted, and has a leaping phrase leading to the reappearance of the melody of the aria. But the music starts to become more frenzied, and the tenor joins in this gathering energy, singing the praises of Armida. The music then becomes swinging and dancing (with pizzicato strings), gathering passion, and the joyful praises of the tenor return. The ending of the aria is more stern, leading to the entry of the chorus, solidly and urgently entreating Rinaldo, reaching a very rhythmic climax. After this has died, we reach a hushed mysterious section, with quiet brass fanfares as the men show Rinaldo the diamond shield. The tenor comments recitative-like, as he sees his reflection and realises the depth of his infatuation , and the chorus returns with the hushed fanfares until Rinaldo relents, more lyrically, and we have strong affirmative music for the line in the chorus "Good, so be it: you must part".

After this a subdued march enters (reminiscent of Beethoven's Choral Symphony), and with a shanty-like theme (cf Wagner). These are repeated twice, becoming more joyful each time, but die away again to the first lines of this section. Then the strings enter, starting a new period, with an aspiring theme; this is developed by the oboe, and the tenor enters, yearning again (thinking of Armida). There is much romantic, yearning from the strings in this wonderful section, which ends with the chorus commenting "shameful bonds".

There follows a brief, stormy call to action, at which the tenor enters, seeing a devil in his love, and the choir comments on the same lines. The storms arise a second time but lead then to a new quiet section, with pizzicato accompaniment. The opening lines are repeated (this entire section is concerned with Rinaldo's feeling of loss at having to leave Armida), and yet again the storms return, with more impetuous accents. These die away into the broad and warm melody of a prayer delivered by the semi-chorus, with the tenor interspersing his own lines still in despair and yearning. Then, the choir are pleading insistently (Quickly") and the tenor is still complaining ("Unlucky wind"). This gradually picks up to a very broad climax and very firm and final chords. This impressive section (from the prayer) is one of the highlights of the work.

But, this is not the end. The final chorus breaks in, and the choir are impetuous. After a prominent descending scale motif, we begin in seafaring mode with two shanty-like themes (with characteristic Brahmsian triplets), the second one a free inversion of the first. This eventually takes us to a new dance-like period where the music is calm and there are typical Brahmsian rhythms. The semi-chorus are here describing the swimming dolphins around the ship. The momentum and tension picks up, and the opening and shanty-like themes return, with the full chorus, and again leading to the gentle dance section, with the tenor. A second time the momentum increases, but with more agitation, as Rinaldo and the men reach their goal. The pace increases, and leads with much joy to the conclusion of the work.