According to numerous reports across Reddit and websites like 9to5Google and Android Police, Messages first beta release, version 4.7, is causing the app to crash immediately on startup.
Android Police says that it has attempted to install the beta on multiple devices without success; in every single case, the app crashes on startup. After conducting a teardown of the 4.7 APK, AP says it believes what’s causing the bug is that the beta release is coded to work with a version of Google Play Services that Google hasn’t rolled out yet. For what it’s worth, this same oversight has happened in the past.
Whatever the case, long story short: don’t install 4.7.
If you’re enrolled in the Messages beta track, make sure to leave the beta track, which you can do so by launching the Google Play Store and navigating to the Google Messages app store page.