According to The Verge, that’s because you downloaded Messenger version 170.0, which was just released yesterday. It seems to have a bug which makes the app crash as soon as you open it, according to many user reports.
The fix is just as simple: Download Messenger version 170.1 right now. It’s brand-new, released today, presumably just to counter that bug. Facebook confirmed to CNET that the new update should solve the issue.