Periodically, as folks are reading through the Scriptures, they see a word or phrase that they haven’t heard much; so they quickly adopt it and begin using it. Some denominational people (and perhaps some brethren?) have taken a fancy to calling themselves ambassadors, since Paul uses the word in two verses. However, a careful reading will discover that he is speaking of himself and the other apostles—not all Christians.
In the Greek are six related words. The root word is presbuteros [Strong #4245], which is used 67 times in the New Testament and translated “elders,” referring to one’s age or the men who oversee the work of the church. The Greek contains a variation, presbutees , which is used three times of aged men, and presbutis , used once for aged women. Presbuterion , appearing three times, also refers to a presbytery or group of men.
This root word is found in two other words, however. Luke uses Presbia  twice—once in 14:32 and once in 19:14. The former refers to a group of men that the King James calls “an ambassage” and the New King James “a delegation.” The latter verse is translated “message” and “delegation” respectively. The delegation consisted of representatives of those who sent them.
The final Greek word under consideration is presbuo , which is translated “ambassadors” in 2 Corinthians 5:20 and Ephesians 6:20. In Ephesians, it is clear that Paul is speaking of himself as an apostle (an official representative of Christ). The one in 2 Corinthians is not as easy to discern, but it does refer to the apostles. Paul writes that God had committed to them the word of reconciliation (2 Cor. 5:19). Christians still try to reconcile men to God through the preaching and teaching of the gospel. Verse 20 then says: “Therefore we are ambassadors for Christ, as though God were pleading through us; we implore you on Christ’s behalf, be reconciled to God.” The apostles stood in the place of Jesus; what they did was by His direct authority. Are Christians today apostles—selected by and specifically sent out by Jesus? No. Neither can we be ambassadors in that regard. We are, however, sent by God’s providence; further we do represent Jesus (if we teach and practice the truth). We do not have the authority of the apostles, however, and cannot be ambassadors or apostles in that sense.
“Now then, we are ambassadors for Christ,
as though God were pleading through us:
we implore you on Christ’s behalf,
be reconciled to God” (2 Cor. 5:20).
“…Pray for me, that utterance may be given to me, that I may
open my mouth boldly to make known the mystery of the gospel,
for which I am an ambassador in chains…”(Eph. 6:19-20).