In today's gospel reading, Jesus says that He wants us to be, "wise as serpents and innocent as doves". It is an interesting combination. Serpents are not usually innocent, and doves, though not a stupid animal, are not considered among the smartest of birds. Also, few people who are wise are often innocent; wisdom and knowledge can corrupt a person and cause them to be quite malicious (think of the idea of a "evil genius"). Furthermore, few people who are innocent are often wise (innocence usually fades by the time someone grows up and gets wisdom), and trying to stay innocent can cause a person to avoid learning wisdom (as in, "if I stay ignorant, then I won't fall into sin"). This is not to say that they never go together, just that is it not the most common scenario.
Thus, it should be obvious that Jesus is giving us a special image that we should pay attention to. We must make sure that as we grow in wisdom, that we remain humble and apply it to ourselves (and not just to everyone else, as though we are called to fix everyone's problems and let our own be ignored). Also we have to work to keep our innocence as an outgrowth of our wisdom. Wisdom can destroy our innocence, and innocence can prevent wisdom.
God's wisdom is always pure, and God's holiness enables innocence. This is what He wants to see in us: people who think rightly, and stay pure from the stains of the world. It is a hard balance to find, and even harder to maintain once it is found. The devil, the world, and our own flesh want to get in the way. Let us pray for these two things in a perfect balance of the righteousness of Christ our Lord. Only then can we deal rightly with this fallen world in which we live.