NOTE: This is a condensed excerpt from my forthcoming (2014) commentary on Philippians.
Paul now shifts to explain his joyful gratitude for the Philippians by expressing the depth of his affection for them: It is right for me to feel this way about you all. Although most English translations give the impression that Paul is speaking of his feelings, he in fact is speaking of something far more significant. A more wooden translation would be “It is right for me to think this way about you all” (cf. NKJV, NET). The verb in question is phroneō, one of the key words in the entire letter. By itself the verb has the broad sense of think, judge, form an opinion, or set one’s mind on something. It is used in a variety of ways here in Philippians, referring to Paul’s mindset towards the Philippians (1:7), the Philippians’ mindset towards each other (2:2, 5; 4:2), the Christian life (3:15) or Paul (4:10), and even the mindset of gospel-opponents (3:19). As such the verb speaks of one’s frame of reference for life, what we today might refer to as a worldview. It is a way of evaluating the world around us and acting in a manner consistent with that mindset. So although this word can include the emotions, the focus is on the mind. Of course, the close relationship between the mind and the emotions means that one’s mindset is both affected by and shapes the emotions.
 In the Greek, this verse actually begins with the conjunction kathōs, which usually expresses a comparison (reflected in KJV, NKJV). Because of the perceived awkwardness, several English translations omit it altogether (NIV, TNIV, ESV, RSV, NRS). But this hides the relationship of 1:7-8 with what comes before (1:3-6) and thus should be retained. Instead of its more common comparative sense, here kathōs expresses cause (cf. BDAG 3; BDF §453.2) as reflected in the NASB and NLT.
 This verb is a distinctly Pauline word; 23 of the 26 NT occurrences are found in his letters (Matt 16:23; Mark 8:33; Acts 28:22; Rom 8:5; 11:20; 12:3 [2x], 16 [2x]; 14:6 [2x]; 15:5; 1 Cor 13:11; 2 Cor 13:11; Gal 5:10; Phil 1:7; 2:2 [2x], 5; 3:15 [2x], 19; 4:2, 10 [2x]; Col 3:2). Ten of those 23 Pauline occurrences are here in Philippians.