A key emphasis in the leadership and management literature is planning and preparation. Sometimes Christians worry about such "business practices." Why not just trust God? Why not just operate in the world in a childlike fashion? Indeed, Jesus says we are to "become like little children" (Matt 18:3). Then again, Jesus himself certainly operated in rather subversive and surprising ways. He criticized religious officials. He did not answer the questions posed to him directly. He said not to throw one's peals before swine (Matt 7:6). He used dramatic symbolic gestures. He appeared in public but then also spend time with just a few of his disciples and also went off by himself. He knew what he was doing when he entered Jerusalem and was arrested. Jesus has served as an inspiration for Gandhi and Martin Luther King Jr. in their mass movements to bring societal change. When one considers this context of subversive, savvy leadership, it should be less surprising that Jesus says to be as "shrewd as snakes" (Matt 10:16).
The Greek word for shrewd or cunning is φρόνιμος phronimos. It is also praised elsewhere in the Synoptic Gospels and translated as "wise:" Matt 7:24; 24:25; 25:2, 4, 8, 9; Lk 12:42; 16:8. The context has to do being prepared. It reminds me of the Scout motto: Be prepared.
Though this word is praised here in Matt 10:16, it is qualified with "innocent as doves" and that is crucial. Good preparation should not become scheming or expedience or cutting corners--doing whatever it takes to get something done regardless if it is right. We are to think ahead and anticipate with might happen. But we are not to manipulate (trick) and deceive. We should be appropriately cunning, shrewd, wise, prepared, and proactive; but we as Christians should also absolutely be people of integrity ("innocent"). If people were to see what occurs behind closed doors via a hidden camera or our email messages or text messages, they would not see anything amiss. They would see us making plans, having meetings, considering what might happen, doing training, taking precautions. They would not be scandalized by our scheming to do things in underhanded, sketchy ways.
Phronimos is also used by the apostle Paul (Rom 11:25; 12:16; 1 Cor 4:10; 10:15; 2 Cor 11:19). When he is using it pejoratively, the sense is that they are "conceited" in the sense of overly wise or overly confident in their own intellects or overly confident in their own plans. They think they have arrived and do not need to learn anything new. This too is a distortion of what it truly means to be shrewd, cunning, wise, and prepared. Someone is not wise if they are so confident they are wise that they are unteachable and arrogant.
In summary, we are to be prepared but not scheming. And we are not to get so confident in our preparation that we think we have nothing else to learn.
So, what does this mean in terms of application? We are to make careful plans but not trick the person we are trying to reach out to. We are to market our programs but we are not to lie about numbers or exaggerate our credentials. We are to appropriately save money but not to build up our barns with massive amounts of savings because we are living in fear. We are to take appropriate precautions about being among outsiders but being shrewd does not mean refusing to leave the comfort and security of home because it is safer. There are people who live utterly in fear for their lives, the lives of their children, and about their financial future. We should be prudent, sober, wise, cautious, prepared but we do not need to live in anxiety and fear.
Proverbs 16:9 reads "In their hearts humans plan their course, but the Lord establishes their steps." This verse puts preparation in perspective. There is sometimes an exaggerated application of this passage that suggests the more naive and less business-like, the more authentic and organic and spiritual. It is a zero sum game. The more humans beings plan, the more God is crowded out. But God's plan has always been to utilize human beings to do his work. Consider God's promise to Abraham to bless him that he might bless others. In this work, it is good for human beings to be shrewd as snakes and innocent as doves.