"Recall that the Jewish lawyer asked Jesus, "What shall I DO?. So, here Jesus tosses the "DO" back to him! Don't misunderstand -- Jesus is not teaching a works based way to inherit eternal life, but He is saying in essence if you do this perfectly, without one sin, then you will attain eternal life. Of course, what Jesus was commanding the lawyer to do was literally impossible and should have served to make him drop to his knees and beg for mercy. Instead, the stubborn, prideful lawyer sought vainly to justify himself or show himself to be righteous, which is exactly what every religion other than Christianity futilely tries to accomplish. They are all unwilling to believe the only work that the Father accepts is the finished work of His Son on the Cross, where He paid the price in full for men's sins ("It is finished" - Jn 19:30)."
- John MacArthur