Why IP and MAC Addresses?

The MAC address is 48bit unique address assigned to any networking/inter networking device, which is embedded on the device and will not change anyway. But the IP may vary each time the device is plugged on to the network (if assigned a dynamic IP address), but there will be only that system on the network with the assigned IP (i.e. address is unique).

MAC address is used only in local communication, i.e. inside a local network only, if it goes out of a network it will use IP address to identify the device/machine.

MAC address is also called Physical address.

As we discussed, the IP address and MAC address are unique, i.e there will be no more than one system with same IP address or same MAC address. So there will be a confusion why to use both addresses?both are unique then why cant use IP or MAC itself?Why both are used in communication?Why the overhead/headache of confusing with both addresses?

Here the answer is,

The MAC address will vary each time the packet of data enters a new network, i.e. the source MAC address and Destination MAC address vary each time the packet reaches a new network, since the physical address is used to locate a system in a local network. The source and destination ip address will remain same always and is not altered with respect to the network changes, the ip should remain same to locate the destination, since the physical (MAC) address varies with network.