I haven't really thought about the power of the word "think" in Philippians 4:8 before.
The Bible indicates that our thought lives ultimately determine our character. Solomon said, "For as he thinks within himself, so he is" (Proverbs 23:7). And old well-known verse puts it this way:
Sow a thought, reap an act;
Sow an act, reap a habit;
Sow a habit, reap a character.
It is because of the importance of our thought lives that Paul said, "Finally, brothers, whatever is true, whatever is noble, whatever is right, whatever is pure, whatever is lovely, whatever is admirable—if anything is excellent or praiseworthy—think about such things" (Philippians 4:8).
As Christians we are no longer to be conformed to the pattern of this world but we are to be renewed in our minds (Romans 12:1-2; Ephesians 4:23; 1 Peter 1:14). Holiness begins in our minds and works out to our actions. This being true, what we allow to enter our minds is critically important.
From chapter twelve of The Pursuit of Holiness by Jerry Bridges.