In the kingdom of heaven, what counts as legal tender? We know that coins with Caesar’s image have value in the kingdom of Caesar. But what is the coin of the realm with God?

A recent documentary answers this question clearly. Called “Beyond the Gates of Splendor,” it tells of five men, working as missionaries, who were killed by natives in Ecuador in the 1950s. These men -- Nate Saint, Ed McCully, Jim Elliot, Roger Youderian, and Pete Fleming -- freshly out of college or the military, married and with young children, idealistically left for the rain forests of the upper Amazon to share the good news of Christ with the natives there.

They were particularly interested in a savage tribe called the Alcas. The Alcas lived without organization or government. Proud and autonomous, they were puppets of their own violent emotions. When an Alca warrior became angry, he would vent his anger by spearing someone, fully expecting to be speared himself some day in return. Anthropologists estimate that in those years six out of 10 Alcas died from homicide.

The missionary men flew a prop plane and made initial contact by dropping food and supplies as gifts. After the Alcas one day returned the drop basket with a parrot inside, apparently offered as a gift, the missionaries deemed it time for direct contact. They landed their plane on a sandbar by a river near the Alca village, and were delighted when almost immediately three Alcas approached and spent the afternoon with them.

But very quickly things went wrong. The missionaries had unwittingly got themselves caught in a fight among the natives. The Alcas who visited them consisted of a young male and female, and their elderly female chaperone. The couple wanted to get married. A powerful warrior in the tribe opposed this: hence he insisted that they never be without their chaperone.

Anyway, the couple used the distraction of the missionaries’ arrival to sneak into the woods alone. When they were seen returning to the village without their chaperone, a violent dispute broke out among the natives. To provide an alibi for themselves, the couple lied and said that they were traveling without their chaperone to flee suddenly, because “the foreigners” had threatened to kill them.

Naturally, when the warriors of the tribe heard this, they went into a wild frenzy of anger. They hurried to the sand bar where the missionaries had set up their camp and killed them all brutally with spears and machetes.

The missionaries kept guns but had decided in advance that they would never use them against the Alcas, even to defend themselves, because, as they put it, “We are ready for heaven, but they are not.”

One might think that the wives of these men, in their sorrow, would have hurried back to the United States with their orphan children as quickly as possible. But not so: they were in this thing just as fully as their husbands. One of them, Betty Elliot, made friends with an Alca who had escaped from the tribe several years earlier. With her cousin, another missionary, Elliot learned the Alca language and then, at the invitation of some Alca women, brought her toddler daughter along and moved in with the tribe.

Betty discovered she had a solidarity with the Alcas. Had her husband been speared? Most other woman in the tribe could say the same.

Betty taught the Alcas that God did not wish men to kill. God had “marked a trail” for us, and, if we followed that trail, then we would find safe lodging when we reached the end. The Alcas accepted this, put aside their killing as belonging to a time when “we lacked understanding,” and they became followers of Christ.

“The blood of the martyrs is the seedbed of the Church,” goes an ancient saying. Within a few years of the bloody deaths of those five missionaries, the Alcas had received the Good News of Christ in a way that those martyrs could not have imagined.

Suppose that God had proposed the following deal to these missionaries: “The Alcas will be converted; and their souls will be saved; but the price that I require of you for this is that you give up your lives.” Wouldn’t all five of those men have accepted that deal immediately?

For all we know God did offer them that deal secretly, in prayer. The wives later reported that, in a radio conversation the evening before the missionaries were slaughtered, one of the men said to his wife, “Pray for us. I think tomorrow is going to be the day.”

The movie answers my earlier question. What is legal tender in the Kingdom of God? Your death. Your self-offering, in imitation of Christ on the cross. That is how a Christian can win graces, convert souls, and re-evangelize the culture.

Not that self-offering needs to take the form of heroic martyrdom. Perhaps even greater is the humble sort that no one would ever notice. The husband who takes a less prestigious job for the sake of his family. The wife who gives up her freedom and perhaps even some physical integrity to give birth to children. The teenager who accepts mockery because he does not go along with his friends when this conflicts with the gospel -- Worth keeping in mind as regards our Lenten “mortification,” or “putting to death.”

Michael Pakaluk is a professor of philosophy at Clark University who resides in Cambridge, Mass.