Why was Mohammed SAW the last prophet if society is still progressing? Intelligent Muslims ONLY.?

Also, I don't understand how muslims believe that Mohammed was the final prophet. That's like saying a kid is done with school after the 5th grade. Humanity is still progressing and Mohammed has not addressed issues that are arising in this changing society with all the advances in technology. A lot of what was said in the Quran was meant for that time, not for eternity. I don't understand why Muslims don't see that. And I don't understand how you can possibly think that Islam is the last religion God will bring. You don't think God will have more divine messengers to address the needs of the future?