What is true is found in God (2 Tim. 2:25), in Christ (Eph. 4:20,21), in the Holy Spirit (John 16:13), and in God’s Word (John 17:17). The Greek term for noble means ‘worthy of respect.’ Believers are to meditate on whatever is worthy of awe and adoration, i.e., the sacred as opposed to the profane. Meditating on what is ‘just’ means those things which are right. The believer is to think in harmony with God’s divine standard of holiness. Things that are pure are those things which are clean and undefiled. Those things which are lovely are those things which are pleasing or amiable; whatever is kind or gracious, in this context. Things that are of good report are those things which are highly regarded or thought well of; what is generally considered reputable in the world such as kindness, courtesy, and respect for others.
Commentary from the MacArthur study Bible, notes for Philippians 4:8.