Believers are ambassadors for Christ

Scripture references

John 17:21–23 (ASV)

21that they may all be one; even as thou, Father, art in me, and I in thee, that they also may be in us: that the world may believe that thou didst send me. 22And the glory which thou hast given me I have given unto them; that they may be one, even as we are one; 23I in them, and thou in me, that they may be perfected into one; that the world may know that thou didst send me, and lovedst them, even as thou lovedst me.

2 Corinthians 5:18–21 (ASV)

18But all things are of God, who reconciled us to himself through Christ, and gave unto us the ministry of reconciliation; 19to wit, that God was in Christ reconciling the world unto himself, not reckoning unto them their trespasses, and having committed unto us the word of reconciliation.

20We are ambassadors therefore on behalf of Christ, as though God were entreating by us: we beseech you on behalf of Christ, be ye reconciled to God. 21Him who knew no sin he made to be sin on our behalf; that we might become the righteousness of God in him.

Colossians 3:17 (ASV)

17And whatsoever ye do, in word or in deed, do all in the name of the Lord Jesus, giving thanks to God the Father through him.

Stories

George Müller's regular visits and kindness made a pretending schoolmaster become a true believer.
For thirteen weeks, George Müller regularly visited a sick man, talking to him about the things of God. In time, the seed of Müller's visits sprung to life, and the man surrendered to Christ, bringing a noticeable change in his life.
A young man who went to preach to a Karen village started by teaching their children to read and write. At first, they were hostile to the message of Christ, but after months of building a relationship with them, and bringing real benefit to their children, they were willing to hear about Jesus. Many of them were converted.