Back in the 1600s, the philosopher René Descartes coined a little phrase that's probably familiar to you: cogito, ergo sum—"I think, therefore I am." The point of that saying is that we validate our existence by the very fact that we can produce thoughts.
Paul the apostle wouldn't disagree with that, but he wouldn't stop there, either. He would say, "I think, therefore I do." That is, whatever you think on, you will eventually do. Good thoughts bear good fruit, bad thoughts bear bad fruit, and you're the gardener.
The Bible consistently describes how our thoughts produce actions—how what we think drives what we do (see John 13:17). And we see this in Paul's words in Philippians 4:8-9. From these two verses, I want to expound on three ways we should think.
1. Think carefully. "Meditate on these things," Paul wrote in verse 8. Meditate in Greek is logizomai, meaning to think or concentrate. The idea is to reason logically so that your actions are based on carefully thought-out principles. Thinking is paramount, according to God's Word (see Proverbs 23:7). What you think about any topic really defines who you are; your life is the product of your thoughts. That's why it's okay to think as a Christian. In fact, Scripture commands us to use our minds (see Isaiah 1:18; Matthew 22:37).
2. Think righteously. Paul laid out the parameters of godly thinking by telling us what we ought to think about: "Whatever things are true, whatever things are noble, whatever things are just, whatever things are pure, whatever things are lovely, whatever things are of good report, if there is any virtue and if there is anything praiseworthy—meditate on these things" (v. 8).
We're bombarded with a lot of different images and messages in the world. We need to be vigilant about what we allow into our minds—what we see, hear, and watch—and make sure we're engaging with and feeding on righteous things, on the unchanging truths of the Bible.
3. Think actively. "The things which you learned and received and heard and saw in me, these do, and the God of peace will be with you" (v. 9). In other words, "Hey, all those things you're meditating on? Actually do them." Thoughts should lead to deeds. You can't separate the thought life from the outward life—the inward thoughts from the outward action. Otherwise you'll get good at hearing truth and immediately dismissing it, having no determination to put it into practice, and your heart will become calloused (see James 1:22-24).
Ultimately, what you ponder is what you're going to practice. There's a relationship between knowing and doing, between doctrine and duty. What you think about is what you're going to do. What you learn is what you're going to live. I pray that God would make us first thinking believers, and then from that we would become doing believers, bearing good and lasting fruit for His kingdom.