The Cantata BWV 151 seems like a treasureable miniature. While it is of a typical length, it has no opening chorus and has a kind of intimacy that makes it the most personal of Bach's Christmas cantatas. The rocking lullaby for soprano with fulte and strings that opens the cantata is one of Bach's most gorgeous works. The gently swaying strings and the elaborate glittery flute part is the closest Bach gets to South German rococo architecture. One can almost see the putti and gold sunbursts of the many churches from this era in Bavaria and Austria. The voice part lies right in the range of both the first violins and solo flute. Together the three create an angelic floating texture of childlike beauty. After the stopped-time quality of the first section, the dazzling quickness of the B section is even more striking. The gavotte character is spiced with dazzling triplet roulades from both the flute and soprano.
The bass recitative begins rejoicing in the birth of Jesus but soon becomes a contemplation on the lowliness of Jesus' status. This theme permeates the rest fo the cantata. The alto aria that follows, with solo violin and all the upper strings in unison, expands on this idea. The unusual texture begins with the strings and solo violin playing a complex chromatic melody over a narching bass line. When the singer enters, the solo violin breaks loose and becomes inextricably, even obsessively, intertwined with the voice part. There is a density and seriousness about the aria that surprises, even when looking at the text. The middle section of the aria lightens up somewhat, but the melancholy chromaticism of the opening keeps insinuating itself into the texture.
The brief happy tenor recitative and the lovely, glowing setting of "Lobt Gott, ihr Christen, alle gleich" that end the cantata don't quite dispel the gloom and unease created by the remarkable alto aria.