Translation
And it is also necessary that he have a good witness from those outside, so that he not fall into reproach and the snare of THE DEVIL.
Paraphrase
And it is also absolutely necessary that he have a good reputation among those outside the church, so that he will not be reviled by them and fall into the trap of THE ONE WHO ACCUSES FALSELY.
A Witness from Those Outside and a Snare of the Devil
Even though the accusations may be false, the real question is, “Are they believable?” The leader of a group of Christians needs to live in such an obviously God-centered way that any lie about him will have no merit because everyone will know that it does not fit the man they know. Of course, there are those who will choose to believe the lie anyway, but if they know the man, they will know it is a lie. Notice that his witness is to come “from” those outside. It is like an echo; he must live before the unbelievers in such a way as to make his conversion from his former days an undeniable fact, and then they will respond by acknowledging his changed life.
How does a snare from the Devil come from this? What is the connection?
It is apparent that Paul was still referring to the fact that the leader of the group of believers could not be “newly planted” because there needed to be sufficient time for those outside the church to see that the leader’s changed life would stick and was not something he could fake for a while. If he was given leadership too early, without fully establishing a testimony of one who had been thoroughly changed, that would leave the door open for various temptations from the Devil. He could get discouraged, he could be tempted to go ahead and live up to his questionable reputation, he could become angry at those who were accusing him, or other possibilities. The point is still that he cannot be new to the faith, rather he needs time to prove to everyone, including those outside, that he is a changed man and above all reproach.