What does it mean that believers are ambassadors for Christ?
Believers are ambassadors for Christ because God has committed to them the word of reconciliation. They represent Him in foreign territory, carrying out His bidding. Their message is that God was in Christ, reconciling the whole world to Himself, not imputing trespasses, so they announce reconciliation to a world at odds with God.
Les explains that reconciliation means taking two parties that have been alienated, that are at odds with one another, and bringing them back into a fellowship. The world tonight is set aside from God, at odds with Him, and enemies of God, yet God has done everything possible to reconcile them to Himself. God was in Christ, reconciling not a few but the world, not imputing their trespasses unto them, and has committed unto us this word of reconciliation. As such, we are ambassadors. We are to carry out God's bidding while we are in foreign territory. The work of the cross was the reconciling of the whole world, and Christ tasted death for every man, not just the few believers but the whole human race.
To wit, that God was in Christ, reconciling the world unto himself, not imputing their trespasses unto them; and hath committed unto us the word of reconciliation.
Now then we are ambassadors for Christ, as though God did beseech you by us: we pray you in Christ’s stead, be ye reconciled to God.