Jesus’ disciples have two great commandments: love God with all their hearts, and love the people in their lives the way they love themselves. Jesus said this is how his identity and mission would be verified—by the existence of a community of irrationally loving disciples.

Those of us who call ourselves “Christians,” who have defined ourselves by affirming right beliefs, often wrestle with having a reputation for exclusivity and judgmentalism, a spirit of us versus them, and a difficulty in embracing the “other.”

However, one of the most striking aspects of Jesus’ approach to people was the way he treated those who were thought to be in the “out” group. Yale theologian Miroslav Volf writes that one of the greatest differences between Jesus and the establishment religious leaders of his time was that they regarded exclusion of the moral or religious “other” as a virtue, whereas Jesus regarded such exclusion as sin. He was strangely welcoming to people normally shunned. His followers learned, often slowly and painfully, to follow in this way.

Bounded sets vs centered sets

So how does one define a follower of Jesus? Here’s one way of thinking about it that I’ve found helpful. An old teacher of mine named Paul Hiebert wrote an article that defined two different ways of sorting objects as either in or out.

One way is by what’s called a “bounded set.” With bounded sets, the way you determine whether an object is in or out is by carefully defining the boundary. For instance, you could determine whether something is a triangle by saying that it must meet the minimum requirements of being a geometric shape that has exactly three distinct sides and three distinct angles. Membership in a bounded set is clear—something is either in or out. Membership in a bounded set is static. A circle will never be a triangle. It cannot become more triangle-y. And a triangle cannot become square-ish. The object either satisfies the criteria or it doesn’t.

Another kind of set is called a “centered set.” Here, objects in the set are defined by their orientation to the center. Membership in the set is dynamic, not static. What matters is movement.

Take, for example, the set “bald people.” The absolute center—the exemplar—is Mr. Clean, the completely hair-free cartoon detergent spokesman. Someone totally outside this group would be the profusely haired Albert Einstein. Now, a baby may be born bald—and so is in the group—but she’s growing hair, so she’s on her way out. On the other hand, a twenty-year-old may have a full head of hair, but it’s beginning to recede, so he’s on his way in. What’s the minimum number of hairs required to be part of the group? Only God—who has numbered the hairs on your head—knows for sure.

A centered set is neither subjective nor vague. It is simply defined in relation to the center as opposed to the boundary.

Inside or outside?

If we think of Christianity as a bounded set, we will focus on the boundary. We will want to define what the necessary and sufficient conditions are for being in. Maybe it’s that someone checked “Christian” as their preferred religion on a survey, or prayed the sinner’s  prayer, or professed a belief that Jesus is divine. Regardless, membership in the group is static. You either are a member or you aren’t, and your status is defined solely by the minimum requirements determined by some outside authority—usually the church or other Christians.

However, the New Testament presents a community of disciples that looks much more like a centered set than a bounded set. The center is Jesus. He defines and incarnates life in the Kingdom of God and makes it available to others. This life is a call to love God with all that you are and to love your neighbor as yourself.

Some people—like certain religious leaders—worked hard to demonstrate that they were in. They knew the Scriptures and paid particular attention to things like Sabbath-keeping, circumcision, and dietary laws. Yet they refused to orient themselves toward Jesus and his kind of agape love. Jesus says they’re actually outside his Kingdom.

Other people, like the sinful woman in Luke 7 or Zacchaeus the tax collector, look a million miles outside the people of God. Yet when they turn toward Jesus, he says things like “Her many sins have been forgiven” (Luke 7:47) and “Today salvation has come to this house” (Luke 19:9).

In fact, what got Jesus into more trouble than anything else is that he often warned people who were sure they were insiders that they were in danger of being outside, and he treated people everyone knew were outsiders as though they might actually be in. Samaritans, lepers, centurions, Canaanite women, divorcées, and more were treated this way.

A dynamic calling

The Scripture writers revel in this sort of thing. When Rahab is identified in the book of Joshua, she is described as “a prostitute named Rahab.” When she’s affirmed in Hebrews as a heroic character, she’s called “the prostitute Rahab.” When she’s cited as an example of good works in James, she’s called “Rahab the prostitute.”

Really? Is there no other adjective available? Rahab the red-head, or the southpaw, or the vegetarian? Clearly, Rahab stands as an example of someone who appears not to fall within the established boundary markers, yet she is part of what God is doing.

If Christianity is a bounded set, then we will want to be very clear about what the necessary and sufficient conditions are to get people inside. Our goal will be to get people to cross the boundary from outside to inside. Once they’re in, any further progress is optional. We can turn our attention to others who we believe have not yet crossed the boundary. If Christianity is a bounded set, we will tend to focus on those issues that differentiate who is in and who is out, rather than those issues that were central to Jesus’ primary concern. We will find ourselves, for example, placing more weight on attitudes about sexual behaviors than about helping the poor—not because Jesus said that sexuality was more important than poverty but because there’s a clearer boundary. Our culture generally affirms concern for the poor but often differs with the church about sexual morality. We will become more concerned with what attitudes and behavior separate us from those outside than about what concerns were most central to Jesus.

However, if following Jesus is about the center, then we will want to constantly orient ourselves toward God and his will and his love. We will want to be ever moving toward it. We will want to invite and help other people to be ever moving toward it. What matters is the orientation and posture of our lives. We are not worried about who is us and who is them. We know that God knows, and that is enough for us. We trust him to do right by each person, including those we love most.

This is why having a centered approach to Jesus is so helpful. It reminds us that following Jesus is not a static religious identity but a dynamic calling that constantly invigorates and challenges us.

Pressing on

Someone once asked cellist Pablo Casals—since he was in his eighties and was the best cellist in the world—why he kept practicing for hours every day. He responded, “Because I think I’m getting better.”

Paul wrote, “Not that I have already obtained all this, or have already been made perfect...But one thing I do: Forgetting what is behind and straining toward what is ahead, I press on toward the goal to win the prize for which God has called me heavenward in Christ Jesus” (Philippians 3:12-14). Paul, you’re already “in”—why do you keep pressing on?

“Because I think I’m getting better.”

In the same letter Paul writes, “Continue to work out your salvation with fear and trembling, for it is God who works in you to will and to act according to his good purpose” (Philippians 2:12-13). Biblical salvation is so much more than having satisfied the minimum requirements. It is the grace-powered redemption of our thoughts and desires and will and action into cosmic meaning and divine love that leads us ever onward and upward.

It’s the dynamic rather than static nature of life that led C.S. Lewis to write, “The world does not consist of 100 percent Christians and 100 percent non-Christians. There are people (a great many of them) who are slowly ceasing to be Christians but who still call themselves by that name: some of them are clergymen. There are other people who are slowly becoming Christians though they do not yet call themselves so...It is some use comparing cats and the mass, because there one knows definitely which is which. Also, an animal does not turn (either slowly or suddenly) from a dog into a cat.”

But human beings are  in the process of “turning into” something—something wonderful or something wicked—all the time. From God’s perspective, of course, there is no ambiguity about human destiny. He promises human beings that we can be accepted and justified and sealed in the Spirit to encourage all who would follow Jesus that this is not ultimately a human enterprise.

Boundaries matter

That’s why, while a centered-set approach may help us understand how we define discipleship,  it remains true that boundaries are indispensable for life—including spiritual life. Divinity schools may need to define the doctrinal boundaries for someone to serve on a faculty. Parents need to be able to say certain behaviors are out of bounds for their children. Churches need to do the same for members. Paul does this when he warns the church in Corinth about tolerating sexual immorality (see 1 Corinthians 5). And perhaps the most famous warnings in religious literature are given by Jesus himself about religious hypocrisy in Matthew 23 (“Woe to you, teachers of the law...”).

In fact, it is precisely because Jesus is so clear about the center (“Love God with all your heart,” “love your neighbor as yourself ”) that he is able to be clear about his warnings when someone is violating love. There is nothing “soft” or ambiguous about his warnings. To the contrary, they’re part of what got him killed. But these warnings did not focus on what were the “boundary marker” issues of his day—circumcision, dietary laws, or Sabbath-keeping. The people he warned were precisely those who prided themselves on being way inside the boundaries while in fact their spiritual trajectory was away from the Kingdom. (“You blind guides! You strain out a gnat but swallow a camel” - Matthew 23:24.)

Champions of grace or soft on doctrine?

When people define “Christian” in terms of having satisfied the minimum entrance requirements for getting into heaven, it always leads to “where to set the bar” debates. Some people set a high bar, saying that only a few radically obedient followers will get into heaven. People who take such a position are considered either champions of radical commitment or exclusionary or legalistic, depending on whether you agree with them.

Others will set a low bar for getting into heaven. They are considered either champions of grace or lax about sin or soft on doctrine, depending on whether you agree with them.

Jesus is radically gracious in his desire to accept and love. He is radically severe in his warnings about sin and God’s judgment. He is radically silent about the minimum amount that a “borderline” person needs to believe or do to get into heaven when they die.

The “bar” Jesus sets for discipleship is not arbitrary. It is not, in that sense, a low bar or a high bar. The bar for pursuing sobriety in Alcoholics Anonymous or for becoming a great cellist or an excellent parent is set by reality. Someone who genuinely wants it above all else will do whatever it takes and consider it a bargain. So it is with disciples who want to live in the Kingdom of God. They will follow Jesus. Their life is centered around him.

That is why, when it comes to the question of who is in with God and who is out, Jesus and the New Testament consistently focus on the center, not on the boundaries.

There is an old tradition on large Australian ranches located on often-dry land that there are two ways of keeping cattle on the ranch. One is to build a fence; the other is to dig a well. What a gift it might be to a world that has become increasingly polarized and politicized if the church would be utterly committed to Jesus as our center. No fences to keep others out, just the life-giving water of Jesus, drawing people ever closer to his presence.

John Ortberg  is the senior pastor at Menlo Church in the USA. John’s teaching centers around how faith in Christ can impact our everyday lives with God. He has written books on spiritual formation including, The Life You’ve Always WantedAll The Places To Go, and If You Want To Walk On Water You've Got To Get Out Of The Boat. John teaches around the world at conferences and churches. The above blog is an extract from his latest book Eternity is Now in Session: A Radical Rediscovery of What Jesus Really Taught about Salvation, Eternity and Getting to the Good Place (Hodder & Stoughton) which is out now