To read the texts click on the texts: 1 Kings 19:9,11-16; Mt 5:27-32
The text of today contains the second (5:27-30) and third (5:31-32) of the six antitheses (5:21-48), which appear in the Sermon on the Mount immediately after the theme. All six while addressing various aspects of the law move the focus away from the letter to the spirit. Each of the six begins similarly i.e. with a juxtaposition of what was said (by God through Moses) and what is now being said (by Jesus to his disciples).
In this pericope, Jesus reaffirms the prohibition against adultery (Exodus 20:14), but goes beyond i.e. to the intention of the heart.
The third antithesis about divorce is related to the earlier one about adultery in subject matter. Deut 24:1-4 assumes the legitimacy of divorce, and in Jewish tradition divorce was relatively easy to obtain. Jesus, however, prohibits divorce. Matthew alone adds the exception clause, not found in Mark 10:2-9 which here is more original and reflects the position of the historical Jesus.
There is sometimes in our understanding of Christianity too much emphasis on what constitutes and does not constitute sin, and on how far we can go before we commit sin. The real question we must ask is how far we must go in love.