Paul is saying that we have a hope of seeing glory, not the kind that was on the face of Moses but the kind which the three apostles saw on the mountain when the Lord revealed himself. Therefore we ought to repay the love of God as far as we can by being more fervent in our love for him, who by cleansing us from our sins has given us this confidence. Now our confidence ought to increase, because what we eventually see will be in proportion to what we now believe.
"Having therefore such a hope, we use great boldness of speech."
For since when he had heard so many and so great things concerning the New [Covenant,] the hearer would be desirous of seeing this glory manifested to the eye, mark whither he hurls him, [even] to the world to come. Wherefore also he brought forward the "hope," saying, "Having therefore such a hope." Such? Of what nature? That we have been counted worthy of greater things than Moses; not we the Apostles only, but also all the faithful. "We use great boldness of speech." Towards whom? Tell me. Towards God, or towards the disciples? Towards you who are receiving instruction, he says; that is, we speak every where with freedom, hiding nothing, withholding nothing, mistrusting nothing, but speaking openly; and we have not feared lest we should wound your eyesight, as Moses did that of the Jews. For that he alluded to this, hear what follows; or rather, it is necessary first to relate the history, for he himself keeps dwelling upon it. What then is the history? When, having received the Tables a second time, Moses came down, a certain glory darting from his countenance shone so much that the Jews were not able to approach and talk with him until he put a veil over his face. And thus it is written in Exodus, [Exodus 34:29-34] "When Moses came down from the Mount, the two Tables [were] in his hands. And Moses knew not that the skin of his countenance was made glorious to behold. And they were afraid to come near him. And Moses called them, and spoke unto them. And when Moses had done speaking with them, he put a veil over his face. But when he went in before the Lord to speak [with Him], he took the veil off until he came out."
Putting them in mind then of this history, he says...
[AD 384] Ambrosiaster on 2 Corinthians 3:12