It is based on 2 Corinthians 5:20 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.
and Ephesians 6:20 (really 6:19-20) 19 Pray also for me, that whenever I speak, words may be given me so that I will fearlessly make known the mystery of the gospel, 20 for which I am an ambassador in chains. Pray that I may declare it fearlessly, as I should.
What exactly is an ambassador? Well I am so glad you asked, here is what Merriam-Webster thinks it is:
\am-ˈba-sə-dər, əm-, im-, -ˌdȯr, -ˈbas-dər\
Definition of AMBASSADOR
: an official envoy; especially : a diplomatic agent of the highest rank accredited to a foreign government or sovereign as the resident representative of his or her own government or sovereign or appointed for a special and often temporary diplomatic assignment
a : an authorized representative or messengerb : an unofficial representative
ambassadors of goodwill>
'an official' is one with authority:
2 Corinthians 10:8 So even if I boast somewhat freely about the authority the Lord gave us for building you up rather than tearing you down, I will not be ashamed of it.
Titus 2:15These, then, are the things you should teach. Encourage and rebuke with all authority. Do not let anyone despise you.
'envoy' is a messenger or representative
Romans 10:14 How, then, can they call on the one they have not believed in? And how can they believe in the one of whom they have not heard? And how can they hear without someone preaching to them?
1 Peter 2:9 But you are a chosen people, a royal priesthood, a holy nation, God’s special possession, that you may declare the praises of him who called you out of darkness into his wonderful light.
Romans 8:29 For those God foreknew he also predestined to be conformed to the image of his Son, that he might be the firstborn among many brothers and sisters.
sent to a 'foreign government':
Philippians 3:20 But our citizenship is in heaven. And we eagerly await a Savior from there, the Lord Jesus Christ,
1 Peter 2:11 11 Dear friends, I urge you, as foreigners and exiles, to abstain from sinful desires, which wage war against your soul. 12 Live such good lives among the pagans that, though they accuse you of doing wrong, they may see your good deeds and glorify God on the day he visits us.
And finally our 'diplomatic assignment':
Matthew 28:19 Therefore go and make disciples of all nations, baptizing them in the name of the Father and of the Son and of the Holy Spirit, 20 and teaching them to obey everything I have commanded you. And surely I am with you always, to the very end of the age.”
Hebrews 13:1-3 1 Keep on loving one another as brothers and sisters. 2 Do not forget to show hospitality to strangers, for by so doing some people have shown hospitality to angels without knowing it. 3 Continue to remember those in prison as if you were together with them in prison, and those who are mistreated as if you yourselves were suffering.
Luke 10:16 “The one who hears you hears me, and the one who rejects you rejects me, and the one who rejects me rejects him who sent me.
So we are ambassadors, Sometimes good, others, well, not so much. But the more we try to remember our 'mission' the better ambassadors we will make.
If you get anything from this get this: Our actions tell people more about our "Lord" than our words do. Proof = Truth, we say we are followers of Christ, great...lets prove it.