The key to the missionary’s message is the atoning sacrifice of Jesus Christ. Take any phase of Christ’s work—the healing phase, the teaching phase, the saving and sanctifying phase. There’s nothing limitless about any of these. But “the Lamb of God, who takes away the sin of the world” (John 1:29)—that is limitless, and that is the missionary’s message. A missionary is one who has soaked in this revelation and has made it the basis of his or her appeal.

The key to the missionary’s message isn’t Jesus Christ’s kindness and goodness. It’s the great limitless significance of the fact that “he is the atoning sacrifice for our sins, and not only for ours but also for the sins of the whole world.” The missionary’s message isn’t patriotic. It has no allegiance to nations or to individuals. It’s meant for the whole world. When the Holy Spirit comes in, he doesn’t consider personal preferences. He simply brings everyone he touches into union with Jesus Christ.

A missionary is one who is wedded to Jesus Christ’s own message. A missionary has no desire to proclaim a personal point of view, only to proclaim the Lamb of God. It’s easier to share personal stories of salvation. It’s easier to be a devotee of divine healing, or of a special type of sanctification, or of the baptism of the Holy Spirit. Paul didn’t say, “Woe to me if I do not preach what the gospel has done for me.” He said, “Woe to me if I do not preach the gospel!” (1 Corinthians 9:16). What is the gospel? Only this: “the Lamb of God, who takes away the sin of the world.”

Wisdom from Oswald

Sincerity means that the appearance and the reality are exactly the same.
Studies in the Sermon on the Mount