Maybe this time?

slack-mathbot/commands.rb

@@ -1,4 +1,4 @@
 require 'slack-mathbot/commands/calculate'
+require 'slack-mathbot/commands/echo'
 require 'slack-mathbot/commands/about'
 require 'slack-mathbot/commands/help'
-require 'slack-mathbot/commands/echo'

slack-mathbot/commands/echo.rb

@@ -0,0 +1,13 @@
+module SlackMathbot
+  module Commands
+    class Echo < SlackRubyBot::Commands::Base
+      command 'echo'
+
+      def self.call(client, data, match)
+        send_message client, data.channel, match[:expression]
+      rescue StandardError => e
+        send_message client, data.channel, "Sorry, #{e.message}."
+      end
+    end
+  end
+end