The Law of God commanded that each person must work to obtain salvation. It was by following the rules and regulations. What God was showing man that he was a sinner separated from God and couldn’t earn salvation. The popular belief in Judaism was you could earn your way to heaven. Even the disciples believed this. So when Jesus told that they couldn’t earn their way to heaven, it through out their beliefs. Peter was shaken and asked Jesus what they supposed to do. Jesus explained that God is to only one who can give a person salvation. Jesus told the disciples because they have left father, mother, sister, brother and family to follow Jesus shall recieve everlasting life. Then He said the first shall be last and the last first. It’s the parable of the marriage supper. With God nothing is impossible.