The dictionary defines “ambassador” as: 1. A diplomatic official of the highest rank appointed and accredited as representative in residence by one government to another.  4. Any authorized messenger or representative.

The followers of Christ have been appointed by God; they have been accredited as representatives of Christ Jesus by God Himself.  We have been authorized as God’s messengers, representing Christ in our world where we live.
What message are you giving others?

(Amplified) 2 Corinthians 5:20-21 “So we are Christ’s ambassadors, God making his appeal as it were through us.  We [as Christ’s personal representatives] beg you for His sake to lay hold of the divine favor [now offered you] and be reconciled to God.
21 For our sake He made Christ [virtually] to be sin Who knew no sin, so that in and through Him we might become [endued with, viewed as being in, and examples of] the righteousness of God [what we ought to be, approved and acceptable and in right relationship with Him by His goodness].”

The followers of Christ have been given a privilege and a responsibility

to be Christ’s representatives in this world.

What message does Christ want you to give to the world?
A prerequisite: “…be reconciled to God.”

Christ was made sin (and He was without sin).  It is only through Christ that you can become the righteousness of God.
What does that mean?  “…the righteousness of God [what we ought to be, approved and acceptable and in right relationship with Him by His goodness].”

Followers of Christ are responsible to be in right relationship with God

and that is by His goodness, not ours.