Below is an excerpt from a commentary I'm writing on the Greek text of Philippians. The section I've copied is a rough first draft treating a key Christological phrase from 2:6.  The commentary will be part of a series called The Exegetical Guidebook to the Greek New Testament (B&H Publications).  It's aimed at seminary grads and pastors who have actually learned and retained their Talbot students, we hope! You can get the abbreviations from Murray Harris's volume on Colossians, but they should be familiar to NT students (e.g., TDNT = "Kittel," etc.).  Enjoy!

The phrase ἐν μορφῇ θεοῦ presents the first crux in our passage. Μορφή (here dat. sg. fem.) is best trs. “form” (most EVV; BDAG 659c). The NIV’s “in very nature God” (“truly God” [CEV]; “God” [NLT]; “possessed of the very nature of God” [H-M 114]) constitutes an interpretation that is neither well supported by the usage of the term in HGk. nor particularly suitable to the surrounding context. Although the term can be used substantially (Plato Phaed. 103e; Resp. 381c; Aristotle Met. 11.1060b; Phys. 2.1.193b; Plut. Quaest. plat. 1003b; Def. orac. 429a; Philo Spec. 1.327–28), there is no semantic component in μορφή that necessarily involves a corresponding “nature” (NIV) or ontology (pace Fee 204; H-M 114). The great majority of instances where μορφή and its cognates occur in HGk. mean simply “outward appearance” (Dan Fabricatore, Form of God, Form of a Servant: An Examination of the Greek Noun μορφή in Philippians 2:6-7 [University Press of America, 2009]; “form, outward appearance, shape” [BDAG 659c]; that “which may be perceived by the senses” [J. Behm, TDNT 4:745-46]).

Jesus changed his appearance at the transfiguration (μετεμορφώθη ἔμπροσθεν αὐτῶν [Matt 17:2; Mark 9:2]), for example, but one would be hard-pressed to maintain that he underwent some kind of ontological transformation during his experience on the mountain. Some texts use μορφή and its cognates in a manner that directly contradicts the inward reality of the object in view. Consider 2 Timothy 2:5: “holding to the outward form of godliness (μόρφωσιν εὐσεβείας) but denying its power.” Similarly, Plutarch compares uneducated rulers to “colossal statues which have a heroic and godlike form (μορφήν) on the outside but inside are full of clay, stone, and lead” (Plut. Ad Princ. Inerud. 780a). In each case, “outward appearance” is solely in view. Examples of μορφή employed in this way abound.

How, then, are we to understand Paul’s reference to Christ “being in the outward appearance of God”? We do not lack for proposals. The most persuasive takes into consideration the following:

(1) A pronounced preoccupation with honor and status in Roman Philippi (Hellerman, Reconstructing Honor, 88-109).

(2) The importance of clothing as a public mark of social status in the Roman world (Hellerman, Reconstructing Honor, 12-19).

(3) The association between glory, clothing, and outward appearance in biblical literature (Luke 9:28–32; 12:27; cf. Matt 6:29; Job 40:10; Sirach 50:11).

(4) A similar grammatical construction in Luke 7:25 (οἱ ἐν ἱματισμῷ ἐνδόξῳ καὶ τρυφῇ ὑπάρχοντες), where royal clothing is in view.

(5) The meanings of τὸ εἶναι ἴσα θεῷ (v. 6), ἁρπαγμόν (v. 6), and the parallel expression μορφὴν δούλου (v. 7)/

In view of these factors, ἐν μορφῇ θεοῦ ὑπάρχων most likely presents a “picture of the preexistent Christ clothed in the garments of divine majesty and splendour” (O’Brien 209; J. Behm, TDNT 4:751). Paul draws attention to Christ’s preincarnate (a better term than “preexistent”) social status, publicly marked out by clothing appropriate to his divine rank (J. Hellerman, “μορφῇ θεοῦ,” 779-97). The image was particularly fitting in a letter intended for a group of Christians in status-conscious Philippi (Hellerman, Reconstructing Honor, 131-33).

This is not to say that an argument for the deity of Christ cannot be made, secondarily, from ἐν μορφῇ θεοῦ ὑπάρχων. As J. Behm notes, the expression portrays Christ clothed in “the garment by which His divine nature may be known” (TDNT 4:752). Paul focuses, however, on Christ’s outward appearance and its implications for rank and status, not upon Christ’s inner or essential nature. See below, on τὸ εἶναι ἴσα θεῷ (v. 6), ἁρπαγμόν (v. 6), and μορφὴν δούλου (v. 7), for further support for reading μορφῇ θεοῦ as a signifier of social status.