Jesus is again confronting the Pharisees. He had just given them the Parable of the Unjust Steward, which speaks about money; thus, this little section is introduced with the Pharisees described as being covetous. Does covetousness have anything to do with the commands of God? How about the tenth commandment?
The Pharisees were offended. Even though Jesus Himself did not say anything directly about covetousness, they were perceptive enough to pick up the drift of His parable. They justified their attitude of covetousness before men who would accept their rationalizations, but as Jesus says in verse 15, they could not escape the scrutiny of God, who judges the heart!
Jesus says that people were pressing into the Kingdom of God. Why? Because Jesus was preaching it, and people were believing the message and repenting. How deeply they believed it is not the point at this time. Crowds were following Jesus, and this enters into His explanation. Jesus warns the Pharisees that, just because people were pressing into the Kingdom of God due to Jesus' preaching of the gospel, they themselves would not pass blithely under the bar of judgment because God would judge them according to the standards given in His law.
Where are those standards given? In the Old Testament! Thus, He says that it is easier for heaven to pass away than for one tittle of the law to pass. Their covetousness would be judged by what was written in the Old Testament. In other words, He could perceive that they were quite sensitive to the standards written in the Old Testament.
To illustrate, He gives an additional principle that He pulls from the Pentateuch, from Genesis 2:24: "Whosoever puts away his wife, and marries another. . . ." Why does He bring that in? Because the Pharisees in actuality had a very cavalier attitude toward the law of God, especially in the area of marriage and divorce. They just brushed it off.
The point is this: Our Savior did not have a cavalier attitude towards the Old Testament. He had every opportunity here to tell these people, "A New Covenant is coming, so do not worry about your sins. We are just going to overlook them." But He did not. He upheld the law and judgment according to it.