The question at the core of morality is this: What makes something right or wrong? Some people talk about rules, some people talk about principles, some people talk about consequences, some talk about virtue. Some people have no restrictions other than "harm none" -- a good desire, to be sure, but a fairly low bar. Setting the highest goal as being "harmless" reads like the part in the Hitchhiker's Guide to the Galaxy where the encyclopedia entry on our planet reads, in its entirety: Harmless. Talk about being damned by faint praise. Granted that "harmless" would be an improvement for some, it's never going to even aspire to positive good.
Some people are suspicious of rules, seeing them as stifling and oppressive. And here is a conflict that comes up time and again: if the rules have no regard for the people, then sooner or later the "no regard for the people" part will make the rules themselves into an immoral force. Rules have the advantage of making people aware of various all-too-predictable ways they can cause harm unintentionally. Even at their best, rules often amount to little more than a serious exercise in considering how to be harmless. Again, granted that we want to give serious thought to how to be harmless, it still leaves us short of doing anything positive.
Here as we look at moraltiy we see some implications of Jesus' teaching on truth. He challenged the generally-accepted idea that truth is impersonal. If truth is impersonal, if the highest reality is impersonal, then principles are more important than people, and morality will put principles above people. But if truth is personal, if ultimate reality is personal, then morality is like the lilies of the field: it beautifies the world rather than enslaving it, beautifies a soul rather than depersonalizing it. In Jesus' teaching, morality returns the value to the world, rather than moving it to another impersonal realm.
Jesus challenged our thinking about morality when he named the highest of all good rules as first, loving God with all our heart, mind, soul, and strength; and second, loving our neighbor as ourselves. If love of God and neighbor is the height of morality, then morality is personal. Love also shows us the way forward to something a little better than being harmless. Paul expounded on Jesus' insight, connecting the dots for his readers: If love does no harm to its neighbor, then love is the fulfillment of the law. We had the answer all along: God's law is written on our hearts.
For those fond of rules, what is the place of the code of moral law? At one point, Jesus makes it explicit that a specific law was made simply for the benefit of humanity: "The Sabbath was made for man, not man for the Sabbath." This particular law was made for us and for our benefit. Of the other moral laws, all of them can be placed under the headings of "love of God" and "love of neighbor." If we view the laws this way, then all laws are made -- and kept -- in full recognition of the person or persons intended to benefit by them. The thought that rules were made for our benefit does not cancel them or make them useless and outdated, but instead shows that they are rightly understood as ways to benefit each other. It shows that using laws as a measuring-stick for moral superiority was always an abuse, that spiritual one-upmanship and cosmic tattletale were always an immoral use of morality.
Jesus' teaching made a connection between love of God and love of neighbor. On the view that humanity is, in a real sense, made in God's image, then it is impossible to separate the two. Morality, then, recognizes all of humanity on the simple basis of that image of God that we share. It follows that all humanity is included, even enemies, so that we are challenged to bless those who curse us, pray for those who persecute us, and repay evil done towards us with good done towards others.