One of the insiders approached Jesus with a warning. Someone that John had not pre-approved was doing the kind of work that John approved of--as long as it was done by the right kind of person.
We can consider several modern-day applications:
sectarianism--should your denomination be allowed to claim to be part of the Body of Christ?
Another problem today is how restrictive should each denomination be in detailing membership requirements? Who gets to decide who is a Christian?
Who gets to decide who gets to join my particular congregation?
Are only Christians allowed to do the work of God in God's name?