Donald English makes a good observation about Jesus' practice of having a purposeful amount of fellowship with "tax collectors and sinners":
"The example of Jesus is again our model. He was sustained by his prayers to the Father, and in his fellowship with his disciples (despite their inadequacy). From these, and his deep knowledge of the Scriptures, he drew sustenance to go into the most unlikely company and not only survive in it but actually win others to faith within it. We are called neither recklessly to risk ourselves nor timidly to secure ourselves, but to find the point of life-giving tension between the two. In that way our worship and fellowship have more point and our witness more depth."
A well-grounded follower of Christ is a person who knows the gospel, the Scriptures as a whole, is part of a strong, supportive community of believers, and has a growing relationship with God through Christ (and the ongoing ministry of the Holy Spirit). Such a person is well-equipped and ready to befriend people who are not believers- those who are lost in sin- in order to share Christ with them. Problems occur, however, when the follower of Christ is not well-grounded before engaging in such fellowship. We (Christians) must hang with unbelieving sinners (not just believing sinners!) in order to share Christ, but not lose sight of Jesus' well-grounded example as English identifies so well.
I always cringe when I hear well meaning parents say they send their kids to this or that school or club or organization "to be a witness". Really? I suppose if their child is a well-grounded follower of Christ (as described above) such engagements might be a worthy mission, however, most young people are in the process of getting well-grounded, not actually well-grounded yet. Heck, how many well-grounded Christian adults to you know these days in evangelicalism? Surely some engagements with unbelievers should be part of training our children, but I fear statements about wanting them to be salt and light before they really know what salt and light are supposed to do is either naive or an excuse.