The "login block-for 100 attempts 15 within 100" is going to block anyone from attempting to remotely access that router (i.e. open a telnet/ssh/rmon whatever connection) for 100 seconds if they see 15 login attempts fail within a period of 100 seconds.
the "security authentication failure rate 3" should have the word log appended to the end. It merely creates a syslog message if you fail to log in 3 times. Should you have it sending syslog messages out to an NMS (i.e. Solarwinds), it will hopefully trigger an alert so you know that somebody is attempting to get into your router.