The scripture passage from John 10 has references first to the thieves whom the sheep should ignore since they know the Shepherd's voice (vss. 1-9), and then to the useless hireling who flees when the wolf comes, unlike the Good Shepherd who lays down his life for the sheep (vss. 11-18). Since the stories are metaphorical, we can figure out the sheep and Good Shepherd easily enough, but exactly who or what the wolf is remains a bit of mystery.
We learn a bit more by considering the passage that likely inspired this account, Ezekiel 34. While it refers to "wild beasts," not wolves per se, we're close enough. We recognize that the wolves in their predation are only interested in satisfying themselves, taking whatever they can from the sheep before ultimately slaughtering them.
In the passage from 1 John 3, we find the direct opposite of the wolfish role as the theme of loving one another is posited as the priority for followers of Jesus, imitating the love - indeed, the sacrificial love, agape love - of Jesus for his sisters and brothers. That's a tough one to swallow, one of several difficult messages to embrace in this passage.
In the end, we find that love is the truest and best weapon for dealing with the wolves. But we also need to be mindful that the wolves are there, among us, not unlike the old cartoon of Ralph the wolf and Sam the sheepdog pictured above. It's just another day on the job for both the wolf and for the one who stands with the sheep. We may not like to identify the wolves among us, but they're there and at work. We're called to be on the job, too, with the love, compassion, and grace of the Lord.
Check out the sermon video below (thanks again, YouTube, for another wonderful still image), and note the downloads below the video panel.