The Gospel just read focuses on a theme that is central to the New Testament but has its roots in the Old.
The subject at hand is the essence and importance of the virtue of righteousness.
Please do not confuse this with self-righteousness!
Self-righteousness is a vice. It is self-aggrandisement. It is what we aptly refer to as being "holier than thou."
Righteousness, on the other hand, though it has taken on various shades of meaning throughout salvation history, can be described as the habit of trying to live according to gospel values while recognizing that we are imperfect and therefore dependent on Divine mercy.
That having been said, we can better understand what Matthew wanted his fellow countrymen to remember.
First that Jesus was the fulfillment of the Law of Moses and that, in the light of his redemptive role, the Law was no longer necessary. Nor, for that matter were the prophets for they too were part of the messianic preparation process.
But, none the less, he implied that they would remain effective until after his own death and resurrection.
Jesus then points out that the Scribes and Pharisees, because they stubbornly and arrogantly refused to turn the page and embrace the new covenant between God and mankind, would be simply left behind, stalled in a time warp.
Jesus sadly proclaims them to be corporately defective in terms of righteousness and, in fact, leaning toward self-righteousness.
It is hard not to sympathize with them. For generations their self-worth was assessed according to the strict observance of literally thousands of minute legalisms augmented by every generation of rabbis.
In short, The Law had become an end in itself. Its original intent and significance were barely recognizable.
It was an example of righteousness having gone haywire and Jesus as quoted in today's Gospel is saying, "Stop! Enough! I am the one for whom you were originally preparing ...I am here! The preparation is over. The Law has served its purpose ...BUT, righteousness remains important, in fact it is so vital that I am taking it to a much higher level. I am taking it to a level that you will never attain but should, none the less, strive toward and in so doing avoid the pitfall of self-righteousness and all semblance of a holier than thou attitude so common among your leaders."
To take but one of his examples, Jesus teaches his hearers not to be satisfied with merely avoiding murder but rather to go straight to the root and curb the anger and insults that lead to aggression.
And here, I suggest is a lesson most of us can apply. If we are to truly grow in holiness, as with Divine help we all can and should do, then we must become aware and get at the root dispositions beneath the forbidden actions to which we refer as "sin."
Speaking as a sinner and as a confessor, let me suggest that the key negative disposition plaguing most of us is inordinate pride that leads to disrespect, that in turn leads classifying individuals and groups as sexual or servile or less. It leads to greed, to envy and to impatience. The list goes on.
The best antidote is, of course humility.
Pray this prayer… "Lord without you I am nothing." Understand this prayer, pray for the grace to mean it and finally to live it or as Jesus said, "Be righteous, truly righteous."