At the very beginning of Facebook's operation in the smartphone era, the main application developed by the company allowed us to perform all activities related to our account, including sending messages to other users. After some time, in 2014, when Messenger became one of the most popular applications for smartphones, Facebook removed the ability to send messages directly from the main Facebook application, and after pressing the icon with conversations, application redirected us to Messenger. Everything seems to indicate that after a few years Facebook plans to re-integrate writing messages with its main application.
Mark Zuckerberg confirmed that his company actually plans to integrate this feature with Facebook's application, but he didn't specify when it could happen. Some users have already boasted their perceptivity on the Internet, because they were able to find in the application code information about mode of Facebook integration with Messenger, which isn't available for using yet. There are many indications that Facebook will allow for text messaging in its main application, and functions such as reactions to messages or voice messages will still remain Messenger's domain.