The cantata begins in a fatalism that is absolute. Unbelief has already been well left behind. The second recitative, furthermore, makes a quick reference to Matthew 7:7-8:
7 Ask, and it shall be given you; seek, and ye shall find; knock, and it shall be opened unto you:
8 For every one that asketh receiveth; and he that seeketh findeth; and to him that knocketh it shall be opened.
The concluding aria cleaves to the sureness of the promise. Bach sweetly pummels this point home with an incessant repetition of patterns, the point overall being: if you believe it, it will happen. Which is probably not the best perspective to adopt in the present world that we find ourselves in.