The original release of Minecraft, now called Minecraft: Java Edition, is soon going to require a Microsoft account to play. The announcement was made on the Minecraft blog, and it means that existing players will start to be moved to Microsoft accounts next year. The move will be mandatory, so you won't be able to play the game if you don't switch to the new account.
To justify the decision to move its player base, Minecraft developer Mojang said that Microsoft accounts offer a range of benefits compared to a regular account. These include additional security thanks to two-factor authentication, linking different games in the Minecraft universe to the same account, improved parental controls, and the ability to block chat messages and invitations.
Aside from using a Microsoft account, there won't be any big changes with the transition. Existing skins and mods will continue to work, and users get to keep their current username. In fact, Microsoft is giving players a small reward for going through the process - a special cape for your character. The company is also teasing that more rewards may be revealed later. You can learn more about the transition in this FAQ.
For new players, the Microsoft account requirement will come into place this fall, meaning you'll need one to create a new account. Because there are a lot of players on the Java Edition of Minecraft (in 2019, the company reported that 30 million copies of the game had been sold), existing players will be moved in batches starting next year. Users will receive emails with instructions on how to make the move when their turn comes.