Ambassadors to Earth

In 2 Corinthians 5 believers are called Christ's ambassadors. That's no small role. It's also a huge privilege, one these verses say we are committed to.
2 Corinthians 5:16-21 "So from now on we regard no one from a worldly point of view. Though we once regarded Christ in this way, we do so no longer. Therefore, if anyone is in Christ, the new creation has come: The old has gone, the new is here! All this is from God, who reconciled us to himself through Christ and gave us the ministry of reconciliation: that God was reconciling the world to himself in Christ, not counting people’s sins against them. And he has committed to us the message of reconciliation. We are therefore Christ’s ambassadors, as though God were making his appeal through us. We implore you on Christ’s behalf: Be reconciled to God. God made him who had no sin to be sin for us, so that in him we might become the righteousness of God."
Let's break this passage down. (For context read the entire 5th chapter of 2 Corinthians here) "So from now on we regard no one from a worldly point of view." - The term not of this earth comes to mind. Something we gain in coming to a Saving knowledge and relationship in Christ is an eternal perspective and adoption in to the family of God. Salvation has given us an eternal perspective.
"Though we once regarded Christ in this way, we do so no longer. Therefore, if anyone is in Christ, the new creation has come: The old has gone, the new is here!" - Because of Christ's death and resurrection, we also die (to the old nature and sin) and are reborn (the new nature) in Christ. Our view shifts from earthly to heavenly.
"All this is from God, who reconciled us to himself through Christ and gave us the ministry of reconciliation: that God was reconciling the world to himself in Christ, not counting people’s sins against them. And he has committed to us the message of reconciliation." - Christ's death on the cross was done for us that we would have atonement and therefore be reconciled:holy before God. Having this done for us, we are to turn around and bring the same message to others.
"We are therefore Christ’s ambassadors, as though God were making his appeal through us. We implore you on Christ’s behalf: Be reconciled to God. God made him who had no sin to be sin for us, so that in him we might become the righteousness of God." - Each of us is an ambassador called to represent God and His interests. God is interested in reconciliation. We've been reconciled to God, He has taken our sin and given us His righteousness. Spread the news.
So the short and sweet: We are Ambassadors on Earth; to Earth. All the time in this lifetime we need to be bringing the message to everyone on Earth.