Two chief reasons:
- The doctrine of common grace
- The doctrine of vocation
The realm of creation is a legitimate sphere in its own right, and it is proper to use the wisdom of a field if it aligns with our general theological framework. This is the essence of the Reformation doctrine of vocation. And it is a natural extension of Romans 12:10, for example, where we are commanded to “give thought to do what is honorable in the sight of all.” This is primarily speaking of cultural practices, but it would no doubt also apply to vocational practices, which are simply a subset of that broader area. There is a respect in Christianity for general wisdom (Proverbs 16:22).
As John Wesley said: “To imagine none can teach you but those who are themselves saved from sin, is a very great and dangerous mistake. Give not place to it for a moment.”
In his book Love Your God with All Your Mind: The Role of Reason in the Life of the Soul, J. P. Moreland points out that the Scriptures explicitly affirm secular thinking in many places:
- Scripture acknowledges the wisdom of cultures outside Israel, including Egypt (Is 19:11-13), the Edomites (Jeremiah 49:7), and the Phoenicians (Zechariah 9:2).
- Scripture recognizes remarkable achievements produced by human wisdom (Job 28:1-11).
- The wisdom of Solomon is compared to that of the “men of the east” and Egypt (1 Kings 4:29-34).
- Paul approvingly quotes pagan philosophers (Acts 17:28).
- Proverbs is filled with examples in which knowledge, even moral and spiritual knowledge, can be gained from studying things in the natural world.
- Jesus once taught that we should know that we are to love our enemies from careful reflection on how the sun and rain behave (Mt 5:44-45).
For more on this, see the chapter “The Giver’s Voice: Seven Benefits of Reading Non-Christian Books” in Tony Reinke’s excellent book Lit!: A Christian Guide to Reading Books.
 For a brief discussion of these, see my post from a recent Global Leadership Summit, “Why Christians Should Learn About Leadership from Both Secular and Christian Thinkers”: //www.whatsbestnext.com/2011/08/why-christians-should-learn-about-leadership-from-both-secular-and-christian-thinkers/.
 John Wesley, A Plain Account of Christian Perfection (London: Epworth Press, 1952; 1st Epworth ed.), 87, quoted in Moreland, Love Your God with All Your Mind, 54.