The birthright was the natural privilege of the firstborn son. Receiving the birthright, the firstborn would become the head of the family, and would have charge of the family, including the family property.
Churches of Christ do not sing a cappella because we dislike other kinds of music. Most of us have as many songs on iPods as the next person. We do not lack financial means to purchase instruments or capable musicians to play them. We are not just trying to be different or stubbornly upholding a longstanding tradition. Why, then, do we sing a cappella?