"I shall sing of the wonders of Jesus." The trumpet reflects the text purely before the singer begins. The oboes and violins join in and play off the trumpet, each finishing each other's musical lines.
You probably know this cantata for its most famous movement -- two verses of what we would call in English "Jesu, Joy of Man's Desiring."
But there is much more brilliance to be explored in this cantata.
Bass aria "Ich will von Jesu Wundern singen" as performed by the Netherlands Bach Society