The fact is, we're not sure Christians can prove to non-Christians that our faith is right and all others are wrong.
We can remove roadblocks to Christian faith that would be created if the Bible were untrustworthy or Jesus were no different from any other religious leader.
By communicating the facts regarding biblical authority and Jesus' divinity, we can show the reasonable and evidential nature of our faith.
In addition, we can point to the unique nature of the Christian movement.
We admit that these facts are not so logically conclusive that they prove the truth of Christianity and the falsehood of all other faiths. Like all empirical and rational evidence, they can encourage our personal commitment, but they cannot compel it.
As we have seen repeatedly, faith in Christ is like all other personal relationships: it requires a commitment transcending the evidence.
Not so much by our logic as by our love. We are called to love our Lord and our neighbor (Matthew 22:34–40). We are promised that all will know that we follow Jesus when they see his love in ours (John 13:35).
Once we testify to the truth we believe and demonstrate God's love in our lives, we can trust the salvation of others to the Holy Spirit.
Human words cannot change human hearts. Only the Spirit can convict us of our sins and need for salvation. Only he can make Jesus real to those who want him. Like witnesses in a courtroom, we are responsible for telling what we have experienced. The verdict is not up to us.
I cannot convince you that Jesus is Lord, but the Holy Spirit can.
It doesn't bother us that only one key will start our cars, so long as that key works. Only Christianity works where we need God's help the most. Our basic problem with God is called "sin." We have all made mistakes and committed sins in our lives. These failures have separated us from a pure and holy God.
The only way to heaven that works is the way that deals with these sins. And only Christianity does that. No other religion offers forgiveness for sins, grace for sinners, and the security of salvation.
Only Jesus saves.