Come unto me, all ye that labour and are heavy laden, and I will give you rest. Matthew 11:29 

We can work ourselves into exhaustion, but we will never work hard enough. We will never be good enough.  Jesus is the only person alive who has ever lived a perfect life. If we come to Him and trust in His work on the Cross then we can have rest because God is the one who has completely done everything. If we have trusted in Jesus and his righteousness has been transferred to our account then we can rest in what He has done for us.