AHHH! MAC Addresses! - Please Try Help Me Understand

Good Day, I was wondering if you could help me out with an understanding of why MAC Addresses are needed exactly, and more importantly, why they need to be sent in Packets?

I did some research, and I generally got the idea that:

Without MAC Addresses, hosts wouldn't be able to see if a packet was actually for them (As they would need to look at the IP Address, and this is layer 3) without accepting the packet, of which it is then taken of the network, if the host sees that it is not for them, I guess they could put it back on the network but this would make processes slow, and generally makes network very insecure?

Another thing I generally summed up my self is when you send a packet over the internet, you have Source and destination IP, and Source and Destination MAC Address, if you had the following packet header information:

SRC IP: 125.55.111.86
DES IP: 111.11.26.77
SRC MAC: 00-09-5B-1F-DB-14
DES MAC: 00-09-52-5E-DF-24

Sending that over the network would mean that the IP (I think) continuously changes to suit the IP Addresses of the routers it goes through, so that it knows which device to send it to, so upon reaching the destination router that will forward the packet onto the end host, the router will look at the MAC Address in the Header, and look it its ARP table, and match the IP corresponding to the MAC, and router will place the destination IP, for example it may be: 192.168.1.10 now, as the destination host and forward the packet down the correct port to the destination host, of which will look at the MAC addresses and accept the packet.

How’s that sound, is this correct, is this the reason to why MAC Addresses are used, have I got anything wrong?

Regards

Steve

 

 

 

 

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