Six whole years after Microsoft acquired Mojang, Minecraft: Java Edition has remained distinct from the Windows 10 / Bedrock version. The former is still the best way to play Minecraft if you want to mod the game, and it's still the only way to access pre-release 'Snapshots' (basically betas for incoming content). But things are finally about to change, with the announcement that come 2021, you'll need a Microsoft account to play the Java Edition.
In its announcement, Mojang notes all the positive changes the new account system will usher in: two-factor authentication, chat and invitation blocking, and improved parental controls. Mojang also assures that all the benefits of Java won't go away: mods and skins can still be created and used, and you'll still be able to play with other Java version folk. That said, the account change won't introduce online play between Java and Bedrock players.
Existing Java users will need to make the "mandatory" transition in early 2021. This will happen in batches, and once you've been transitioned you'll receive a free cape. As for Java newcomers, starting some time this month they'll be prompted to create a Microsoft account, rather than a Mojang one. The process doesn't seem very complicated, and this FAQ addresses most aspects of the move.
Check out the announcement video below, which shows you what the free cape will look like.