If your log rule matches your drop rule place it before the drop rule. You will also need to create a new logging rule (for the “firewall” topic) that will tell the system which action to take with the messages.
I.e. if you have a syslog server, create a new logging action that points to syslog. Then you will create the rule of topic “firewall” that points to the action that you just created for the syslog server.