The Lord was answering a question from a Pharisee lawyer.  These were a religious sect whose the members made great showy displays of morality and piety. They were sticklers of the letter of the Law. They, also, made long prayers on the street corners and contributed largely to the support of the priests and of the Temple. So particular were they in their habits of cleanliness, that the Lord sarcastically said of them on one occasion that they strained at a gnat and swallowed a camel! Yes; they were a self-righteous and self-loving class who swallowed the camel of hypocrisy and injustice, but strained at the observance of the mere letter of the law. 

For one of the most scathing judgments of any class to be found in any language, read the 23rd chapter of Matthew.

Are there people, today, who make great outward moral and religious shows of righteousness? Then let them think about the awful denunciations of the Lord. 

How fitting, then, was the Master's reply to this lawyer! Jesus' answer summed up all the instructions of the Law and the Prophets (the faithful servants and teachers of the law) in one word – Love. Love is the very essence or spirit of God's commands. The 10 Commandments were engraved on two tablets of stone. The first tablet contained the Laws relating to man's obligations to his Creator. The other tablet set forth the duties of man toward his fellowman. Therefore, "Thou shalt love thy God with all thine heart…and love thy neighbor as thyself."