“They’ll know we are Christians by our love.” So went the hymn popular in the early days of the renewed liturgy following Vatican II. It seems from Paul’s letter that that was exactly what happened in his foundation at Thessalonika, the second of his churches in Europe. In this passage Paul encourages his Thessalonians to continue in the pattern of loving behavior for which he had already commended them earlier in this same letter. Their care for one another was so impressive that it was known all over northern Greece at the time Paul wrote this, his first ever “epistle”.

How does the Church grow and spread? The impetus is, of course, God’s. The Acts of the Apostles stresses that point repeatedly. But God chooses to act in an incarnate way, that is in a “fleshly” way – not just in the man, Jesus, but in the Christian community, acting in human ways. Rodney Stark, the sociologist of religion, notes that individual behavior in the Mediterranean world was typically “every person for him/herself”. Christians who loved one another stood out – were different. The Greek word for “love” that Paul uses here, as in most places in the New Testament, does not mean affection or romantic attraction, it means concern for others, even, if necessary, at the expense of self.

Stark tells us that, on the occasions of plagues that occasionally swept across the Mediterranean, the pattern was to run for one’s life out to the countryside, abandoning the sick to care for themselves or (mostly) to die. Typically the small pockets of Christians didn’t do that. They stayed with their sick, nursed them, and often cared for their abandoned pagan neighbors as well. There were two big consequences. First, because nursing helps, physically as well as emotionally, fewer Christians than pagans died. Second, pagans, seeing this behavior, or perhaps being the beneficiaries thereof, said “I would like to be like that.” Care for others preaches a powerful sermon.

Well, that was then; this is now. An interesting, even edifying, story. But what does it mean for us? That doesn’t happen anymore, does it?

It turns out it does. There were about three million Christians in China in 1949, when the Communists took control of the country, repressed religion, and imprisoned or deported all foreign missionaries. Since that time, with essentially no missionary intervention from outside, that number has grown, despite periodic spasms of repression and persecution, to about 100 million – in numbers, certainly, the largest growth in Christian community in history – occurring right under our noses and in our own times. How did it happen? The Holy Spirit, of course, always. But once again, the Spirit incarnate in Christian communities.

The stories that have come out of China read just like the stories in Acts – care for one another, concern for neighbor, commitment to spreading the good news to others, even devoting one’s life to the work. Non-Christian Chinese, literally by the millions, have responded, saying “I’d like to be like that, too.”

Paul’s encouragement of the Thessalonians in today’s reading is simply an echo of Jesus’ own explicit statement: “A new commandment I give to you that you love one another, even as I have loved you . . . By this everyone will know you are my disciples.” (John 13:34–35).