Being Wise as Serpents, Or Using What Wisdom You Have

From C.S. Lewis, Mere Christianity:
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Prudence means practical common sense, taking the trouble to think out what you are doing and what is likely to come of it. Nowadays most people hardly think of Prudence as one of the 'virtues'. In fact, because Christ said we could only get into His world by being like children, many Christians have the idea that, provided you are 'good', it does not matter being a fool. But that is a misunderstanding. In the first place, as St. Paul points out, Christ never meant that we were to remain children in intelligence: on the contrary. He told us to be not only 'as harmless as doves', but also 'as wise as serpents'. He wants a child's heart, but a grown-up's head. He wants us to be simple, single-minded, affectionate, and teachable, as good children are; but He also wants every bit of intelligence we have to be alert at its job, and first-class fighting trim. The fact that you are giving money to a charity does not mean that you need not try to find out whether that charity is a fraud or not. The fact that what you are thinking about is God Himself (for example, when you are praying) does not mean that you can be content with the same babyish ideas which you had when you were five-years-old. It is, of course, quite true that God will not love you any less, or have less use for you, if you happen to have been born with a very second-rate brain. He has room for people with very little sense, but He wants every one to use what sense they have.