This is a parallel with Jesus' famous Commission of the Twelve in Matthew 10:16: Behold, I am sending you out as sheep in the midst of wolves, so be wise as serpents and innocent as doves. On the surface, Thomas is using the saying in a similar way, although his notion of wolves may be different. Scholars and Pharisees would have been two kinds of Jewish authorities at the time. These figures are being criticized for not following a wisdom tradition as the Thomas community does (they will not help you and they will mislead others). It's not clear, though, that this advice is being given to missionaries as is in Matthew 10:16. The metaphor of sly serpents is striking since snakes were sometimes associated with gnostic traditions. But the overall meaning of the saying seems similar to the version in Matthew: be ready to outwit the wolves without becoming a wolf yourself. For the record, Matthew 10:16 is an important saying to me--something of a life verse, I suppose.