For some network layer protocols, a network administrator assigns network host addresses according to some predetermined internetwork addressing plan. Addressing occurs at the network layer. This is similar to the function of the host portion of an address. The host portion tells the router to which specific device it should deliver a packet. Without network layer addressing, routing can not take place.
Routers require network addresses to ensure proper delivery of packets.
Without some hierarchical addressing structure, packets would not be able to travel across an internetwork. In a similar way, without some hierarchical structure to telephone numbers, postal addresses, or transportation systems, there would not be a smooth delivery of the goods and services.