(20) He does not come with letters of recommendation (2 Cor 3:1-3); he does not show the power and glory that ought to accompany an emissary of God.
Paul somewhat later uses the metaphor of God's ambassador to describe his ministry (2 Cor 5:20).
Paul hints at this hope in the citations of Isa 55:10 and Hos 10:13 in 2 Cor 9:10 and expresses it even more clearly in Rom 11:13-32.
"Now when I came to Troas for the gospel of Christ and a door was opened in the Lord for me, I had no ease for my spirit because I did not find Titus, my brother, there; on the contrary, giving some directives to them I went off to Macedonia (2 Cor 2:12-13).
His earliest letter is addressed to the Thessalonians from Paul, Silvanus, and Timothy (1 Thess 1:1), while he lists Sosthenes in 1 Cor 1:1 and Timothy in 2 Cor 1:1 and Phil 1:1 as co-senders of those letters.
The first suggests the word "Apostle" (frequent in Paul), the second the verb [TEXT NOT REPRODUCIBLE IN ASCII] (2 Cor 5:20, its only occurrence in the New Testament), as terms in Paul possibly equivalent in a broad sense to mission, though each has specific social implications.
On his low rhetorical ability and weak body, see 2 Cor 10:10.