2 Corinthians 5:20 (NKJV)
Every country that wants to have official representation in another country sends an ambassador to that other nation. Ambassadors are sent by their home nation to promote that country and the interests of that place and that government, not to go and promote themselves or their own interests. No good ambassador would work against their home nation or do things that would be a bad representation of where they come from. Good ambassadors maintain good contact with their home country, and they only say and do the things given to them by the leaders of their home nation
In 2 Corinthians 5:20 Paul talked about being an ambassador for Christ. He said that as he did his work, it was as though God was pleading through him that people would be reconciled to God. Paul was not just doing or saying something that was his own idea or even necessarily his own desire. Paul understood that he was an ambassador, representing God to the people he came into contact with. But, being an ambassador for Christ is not just something that was limited to the Apostle Paul. We may not be an apostle like he was, but we can still share the Gospel message with the people we meet.
Earlier in 2 Corinthians 5, Paul talked about having the ministry of reconciliation, telling people the good news that, because of Jesus, God is not holding their sin against them. This is what it means to be an ambassador for Christ. Some people may be called to different types of work in the Body of Christ, but we are all ambassadors for Christ. As ambassadors for Christ we must represent Him and His message, not ourselves or our interests. We need to live our lives with the understanding that we are an ambassador for Christ, we go where He leads us and do and say what He wants; this is something that every believer can and should do