Here's why:

* Early Development: The neural tube forms during the third week of human development, a process called neurulation.

* Foundation of the Nervous System: The neural tube is the precursor to the central nervous system, which includes the brain and spinal cord.

* Essential for Function: The nervous system is essential for all other organ systems to develop and function properly. It controls everything from movement and sensation to breathing and heartbeat.

While other systems like the cardiovascular and digestive systems start to form shortly after, the neural tube is the first major organ system to take shape and is crucial for the embryo's development.