The Orgelbüchlein ("Little Organ Book") BWV 599-644 is a collection of 46 chorale preludes for organ written by Johann Sebastian Bach. All but three of them were composed during the period 1708–1717, while Bach was court organist at the ducal court in Weimar. The remaining three, along with a short two-bar fragment, were added in 1726 or later, after Bach's appointment as cantor at the Thomasschule in Leipzig.

The collection was originally planned as a set of 164 chorale preludes spanning the whole liturgical year. The chorale preludes form the first of Bach's masterpieces for organ with a mature compositional style in marked contrast to his previous compositions for the instrument. Although each of them takes a known Lutheran chorale and adds a motivic accompaniment, Bach explored a wide diversity of forms in the Orgelbüchlein. Many of the chorale preludes are short and in four parts, requiring only a single keyboard and pedal, with an unadorned cantus firmus. Others involve two keyboards and pedal: these include several canons, four ornamental four-part preludes, with elaborately decorated chorale lines, and a single chorale prelude in trio sonata form. The Orgelbüchlein has a four-fold purpose: it is a collection of organ music for church services, a treatise on composition, a religious statement, and an organ-playing manual.

Puer natus in Bethlehem (A child is born in Bethlehem) is a medieval Latin Christmas hymn. The thirteenth-century text is traditionally associated with a fourteenth-century tune of the same name. Bach created a Christmas choral in the Orgelbüchlein with this hymn (BWV 602). Interestingly, Bach includes a repeat at the last bar, indicating the entire chorale is to be played twice, the only such instance in the collection. The piece is on the brief side without it, but not excessively so by Orgelbüchlein standards, so the reason for the repeat is not obvious. Is Bach trying to emphasize the second person of the Trinity in this Christmas chorale? That's pure speculation; I don't know. In any case, all the better: one gets to hear this delightful setting twice, and in this realization, I have set the two repetitions with different scoring. The first time through the verse emphasizes the cantus firmus and the bass, while on the repeat. In my arrangement, I have tried to bring out the interplay in the inner voices, while also adding a bit of heft to the outer voices for balance.

This is one of the gems of the Orgelbüchlein, a timeless evocation of the boy in Bethlehem by the genius of Bach.

Source: Wikipedia (https://en.wikipedia.org/wiki/Puer_natus_in_Bethlehem) .

Although originally created for Organ, I created this Modern Interpretation of the Choral Prelude (BWV 603): "Puer natus in Bethlehem" (A child is born in Bethlehem) for Double-Reed Quartet (2 Oboes, English Horn & Bassoon).