Paul informs us that christians don't need letters of introductions, because they're written in their hearts. We're also told that all our competences are given by god. He promises a new covenant with god, given not by a set of laws, but by the holy spirit. Much easier for getting converts that way. Also good? Telling people the old way leads to death. And that they can get to know god through the new way.
Now, with all our newfound glory, we can be direct, unlike Moses, who put a veil over his face so people wouldn't see the shine of god fading. Apparently the people of Israel still wear this veil over their hearts. If they turn to god, though, the veil will be lifted.
Now that we have this awesome new relationship with god, we need to be forthright in telling people about it. If their hearts remain veiled, Satan did it. After all, they aren't preaching about themselves, but about Jesus, because god turned a light on in our hearts. This allows us to be troubled but not distressed, perplexed but not despairing, persecuted but not foresaken, cast down but not destroyed. Our suffering is supposed to remind us of Jesus, and give life to others.