Able to speak with someone about a subject where they completely disagree without making the other person feel as if they must be on the offensive all the time.
The shield of faith is a shield that we hold up within ourselves because we feel that something is true.
They also feel that their beliefs are true and when those beliefs are felt to be openly challenged their shield of faith is raised.
It is the great soul winner that can slowly move an "adversary" over to further truth.
When someone goes on the offensive they have ceased to hear what you say. Interestingly enough when they cease to believe that you are hearing what they say then they tend to go on the offensive as well.
I think the Bible sums it up more succinctly than I.
Pro 11:30 The fruit of the righteous [is] a tree of life; and he that winneth souls [is] wise.
Mat 10:16 Behold, I send you forth as sheep in the midst of wolves: be ye therefore wise as serpents, and harmless as doves.