The Sermon on the Mount unveils a new understanding of human flourishing

A6 | 15 FEBRUARY 2026 | MATTHEW 5:17-37

The Sermon on the Mount, which continues in this week’s gospel, has generated more comment, commentary and criticism, both within and outside the Church, than any other part of the Christian Gospels. One of the earliest Christian texts, the Didache or Teaching of the Twelve Apostles, for instance, a second century (possibly first-century) handbook, discovered only in 1873, refers to the Sermon eight times in its opening section alone. When St Justin Martyr (100-165), the first known philosopher to have become a Christian, defended Christianity’s noble and humane morality before the Roman emperor, Antoninus Pius (86-161), he too quoted copiously from the Sermon. On the other hand, Nietzsche (1844-1900) despised the “slave-morality” he descried in its ethic of non-resistance, self-denial and neighbourly love. To him, these “weaknesses” were obstacles to true human greatness, exemplified in those Übermenschen who say, “Amen to life, not the words of a god”.

In this particular passage of Matthew’s gospel, the most Jewish of the four, Jesus stresses that he is fulfilling the Law of Moses, not replacing it: “Do not imagine that I have come to abolish the Law or the Prophets. I have come not to abolish but to complete them. I tell you solemnly, till heaven and earth disappear, not one jot, not one tittle, shall disappear from the Law until its purpose is achieved” – a “jot” being the smallest letter in Hebrew, and a “tittle”, the dot over a letter. But what Matthew also makes clear is that the “fulfilment” of the Law to which he refers is a restoration of its true life-giving spirit, for so long obscured by slavish observance of its deadening letter.

Matthew was countering, however, not just Jewish legalism but early Christian antinomianism. There were some, Marcion (100 160), for instance, a wealthy Black Sea convert, who would later reject the Old Testament entirely, who argued that the Law and the gospel were incompatible. For Marcion, even the gospels were unsatisfactory texts: he wanted to rationalise what he considered embarrassing inconsistencies among them by retaining only Luke’s gospel, considered, rightly, the most elegant, and Paul’s letters.

Steering a middle course between legalism and antinomianism, Matthew illustrates in a set of antitheses that mirror the Beatitudes how Jesus’ teaching, far from opposing the Law, deepens its meaning by distinguishing between external behaviour and the inner dispositions that give to our behaviour. The actual topics raised had been hotly debated in Jewish circles and were still controversial in Jesus’ day. Characteristically, Jesus cuts to the heart of each.

So, for instance, he makes it clear that the point of the command not to kill wasn’t just that we should refrain from killing, while accepting that everything short of killing was permissible, but that we should never even wish someone dead. It is the wrath that would wish someone dead that is at the root of the violence that kills them. Jesus was not, however, outlawing “righteous anger”. Aquinas, for instance, thought that it is the mark of a virtuous person that they are angered by injustice. But this is entirely different from the seething anger that leads so easily to violence. Quite apart from the harm done to others, we ourselves are diminished, rendered less than human, by bearing such ill-will towards another person. Pragmatically, even, anger is often simply counterproductive. “Be calm in arguing, for fierceness makes error a fault and truth discourtesy”, as George Herbert in The Church Porch advises.

The reference to sexual impropriety would have been even more counter-cultural in Jesus’ time than it is in our own. Saying “no” to lustful thoughts and desires would now strike many as unhealthy repression. But Jesus teaches here that the damage is done not just by acting on such thoughts: the thoughts themselves, whether they materialise in action or not, de-humanise the thinker as much as they demean the object, just as much as hateful and bitter thoughts. The key, however, is not primarily restraint, but to see with different eyes; to celebrate the goodness and beauty of God’s creation in everybody. Restraint and discipline play their part, of course, given how lust and anger can be so overpowering and all-consuming, skewing judgment and issuing in the unthinkable, as Shakespeare and Donne knew well.

All this the world well knows; yet none knows well

To shun the heaven that leads men to this hell.

Sonnet 129

Reason, your viceroy in me, me should defend,

But is captived, and proves weak or untrue.

Holy Sonnet 14

Jesus’ opposition to the swearing of oaths was a deepening of what is said in the Ten Commandments about not taking the Lord’s name in vain. He is not suggesting that oaths demean God, rather that they should be redundant. Simple honesty and integrity should obviate any need of oaths. We should always mean what we say and say only what we mean; with the caveat, of course, that speaking honestly sometimes means saying less rather than more.

So, in the Sermon on the Mount Jesus is not just delivering novel moral prescriptions but unveiling a new understanding of human flourishing, which is what morality is concerned with. He directs our attention to the work of the Spirit, transforming us from within, giving rise to a way of living that fulfils our God-given nature, at the heart of which, Aquinas says, is “the grace of the Holy Spirit…shown forth by faith working through love.” (ST 1a2ae 108.1)

Jesus will later say that the whole of the Law is summed up in love of God and love of neighbour; and in John’s gospel he could not be more explicit: “I give you a new commandment: love one another as I have loved you.” (John 13:4) But to dispel any hint of sentimentalism, he will also tell us that we are to love even our enemies, as he does.