Ministry is not always easy. In fact, it can be dangerous. But Jesus does not necessarily expect us to be needless martyrs.
Jesus made it clear there would be times when people might want to destroy us just as wolves prey upon sheep. Just as sheep are no match for wolves, so the powers of darkness have numerous evil weapons at their disposal with which to inflict great harm upon us.
The key is to be wise as serpents. Serpents are not necessarily strong. Nor can they withstand the power of larger animals. But they are cunning. In this instruction, Jesus revealed his pragmatic wisdom. He alerted His disciples that they were not to needlessly become victims when it could be avoided. There might be occasions when it was wise to watch our words or actions so it did not bring harm our way. This cannot always be avoided. But it should be, when possible. And, if we must endure suffering for the cause of Christ, there is a wise way to conduct ourselves even then.