'Credentials' in the Bible

Jesus answered them, “I have told you so, yet you do not believe. The works that I do in My Father’s name testify concerning Me [they are My credentials and the evidence declaring who I am].

When I arrive, I will send whomever you approve with letters [of authorization] to take your gift [of charity and love] to Jerusalem;

Are we starting to commend ourselves again? Or do we need, like some [false teachers], letters of recommendation to you or from you? [No!]

You are our letter [of recommendation], written in our hearts, recognized and read by everyone.