"Finally, brethren, whatsoever things are true, whatsoever things are honest, whatsoever things are just, whatsoever things are pure, whatsoever things are lovely, whatsoever things are of good report; if there be any virtue, and if there be any praise, think on these things." (Phil. 4:8)
Pure means clean. If our thoughts are pure, then it only follows that our actions will be pure. The point about thinking on these things is to put them into practice (v.9 "Those things...do..."). Every Christian is called to purity. We are to love God and others out of a pure heart (1 Tim. 1:5). We are to present the Gospel with a pure conscience (1 Tim. 3:9). We are to keep ourselves pure, understanding that we can potentially be participating in other's sin (2 Tim. 1:3).
"Whatsoever things are lovely." The world thinks of loveliness as being soft and some kind emotion that generates warm fuzzies. However the Bible defines for us what love really is, this helps us understand from a Biblical perspective what then is lovely. In John 14:15 Jesus said: "If ye love me, keep my commandments." True love is doing what God says to do. Therefore if we are to think and act on things that are lovely, then we must run our decisions through the Word of God. Love that is void of obedience is not lovely. God is interested in aesthetics. Somehow, there is a stupid philosophy that says things done for God does not have to be the best. I disagree. I think God is worthy of our finest service all the time. Doing our dead level best, in clothing, in singing, in music, in giving, in preaching, in teaching, in reading the Bible, in witnessing, ought to stem from a heart that truly thinks on things lovely.
"Good report" means reputable (Strong) or sounding well (Thayer). When God finished his creative work, He evaluated it and pronounced them 'good.' We ought to do or to practice virtues in our lives that can bring others to an appriciation of our God. We must constantly be on our guard to proctect our reputation before a fallen world, lest the name of our God be evil spoken of. What a priveledge it is to be called a "Christian." I remember reading a Spurgeon sermon, where Spurgeon said in essence, we should not worry about our Lord Jesus since He will never betray us, rather we should worry that our lives may betray the Lord Jesus we say we serve.