Villagers have jobs, so why shouldn't the players have some as well?

When you start a new world, you'll be greeted with a screen that has multiple options for different jobs. It starts with only a few: Farmer, Builder, Miner, or Fighter. Each job will give you different bonuses depending on which you choose.

The farmer will get more XP when gathering crops and breeding animals, and will receive more crops when harvesting.

Builders will have 3 more Inventory slots (to hold more blocks) and be able to break things slightly faster.

Miners will get more XP when mining, pickaxes will automatically have more durability, and smelting ores will take less time, even in a blast furnace!

Fighters will do more attack damage, have a highter likelihood of receiving better drops from mobs, and get more XP.

You can level up in different careers after spending XP, which can give higher bonuses and unlock specialized branches for the different careers, or reveal totally new jobs!

I know some of these are a bit OP, and this would be really different from vanilla Minecraft, so this would probably be better as a Mod