I get the debugging experience, as I've already found it pleasant and painless compared to the difficulty of setting debugging environments in other languages. But for the messages first approach and thinness, what's the real world benefit in practice?
You can intercept and modify messages on the fly. This helps a lot if you want to update legacy code, but don't want to break other classes that use the same call. It also allows for modularization more easily. I have a project that receives data from a bunch of sources, so I have a class for each source (this is simplified). To make it much easier to add a new one, which happens pretty regularly, the code that calls the processor checks all the classes in a specific folder for a certain function (`.respond_to?`) and then gets the right one for the data type. This means that to add a new source I have to change 0 lines of legacy code, just drop the new class file in the right place and it works.
Ruby makes message passing first class. That just changes how you think about programs. In exchange you give up passing functions so our anonymous functions are our blocks (actually just another object that can receive messages). So you don't `list(something)` you `something.list` and that lets you change what `.list` does depending on who `something` is very easily.
Ruby's defining feature is that the line between language author and program author is razer thin. You can completely change the language yourself by extending core classes. This is why we have `1.day` in Rails even though its not supported in the main language. DHH (author of Rails) could add that without consulting Matz (author of Ruby). So lots of stuff gets prioritized to make developers happy because its easy to add.
In Ruby the messages you receive are passed up the chain of ancestors. Your ancestors are a linked list of classes going back to a root class like `Object`. You can modify this linked list at will with mixins and inheritance with complete control (should I go before or after this other receiver).
Ruby's REPL and debugging experience is amazing. I often keep one tab with an `irb` or `rails console` open to sketch things while developing the code for it elsewhere. I'm also always inside a debugger to figure things out. When I'm in Rust or Python I'm met with a very different environment.