I've been re-reading Tim Keller's paper on the centrality of the gospel that I posted last month (thus the quote from yesterday). In it, he talks about how a firm grasp of the gospel works some characteristics into us that are immensely valuable in our witness to non-Christians:
1. We are compelled to share the gospel out of generosity and love, not guilt.
2. We are free from fear of being ridiculed by others, since we already have the favor of God by grace.
3. There is a humility in our dealings with others, because we know we are saved only by grace alone, not because of our superior insight or character.
4. We are hopeful about anyone, even the "hard cases", because we were saved only by grace, not because we were likely to become Christians.
5. We are courteous and careful with people. We don't have to push or coerce them, for it is only God's grace that opens hearts, not our eloquence or persistence or even their openness.
So drink deeply from the fountain of God's love revealed in the gospel, and get out there and tell someone about Jesus!