The Pharisees were obsessed by rules. They believed that keeping the rules would earn them favour with God: the more diligent they were in their religious practices, the more God would be pleased, or so they thought. They had forgotten that God demanded that every law was kept perfectly all the time and that even the smallest sin was enough to invalidate their salvation. Yes, they had the sacrifices to atone for their sin temporarily, but there was no sacrifice for intentional sin. Therefore, everybody who relies on the Law will be condemned (Romans 3:23).
 
By asking Jesus to name the greatest commandment, the Pharisees wanted Jesus to side with them against the Sadducees (who did not give the Old Testament Law too much literal significance). They also wanted to see whether He would agree with their idea of which laws were the greatest - it was a popular debate at the time. But, of course, Jesus was not caught out.
 
Instead of citing a particular commandment, Jesus summarised the purpose of the Old Testament Law - to bring people into relationship with God. He did not want their religious duty but their love; neither did He want legalistic nit-picking among religious communities, but genuine loving relationships and sacrificial lifestyles. Jesus wanted the Pharisees to understand that legalism was not enough. Without love they had no future with God at all.
 
That is the reason for the gospel. We are all sinners and cannot justify ourselves in God's sight. That is why Jesus became the one perfect sacrifice for the sins of the world. Those who trust in Him will enter a relationship with God. That is so different from Christ-less religion. Whichever religion you look at, it has a sort of moral ladder to climb, hopeful of pleasing God. But that is not the Christian life. We start to enter a relationship with Him once we admit we are out of relationship, and experience the relationship once we welcome Him as Saviour and Lord. Look at www.crosscheck.org.uk and share it with your friends. It will help them to find this relationship also.