“The verb here rendered ‘emptied’ is in constant use in a metaphorical sense (so only in the New Testament: Romans. iv.14; I Corinthians i.17; ix.15; II Corinthians ix.3) and cannot here be taken literally. This is already apparent from the definition of the manner in which the ‘emptying’ is said to have been accomplished, supplied by the modal clause which is at once attached: by ‘taking the form of a servant.’ You cannot ‘empty’ by ‘taking’ — adding. It is equally apparent, however, from the strength of the emphasis which, by its position, is thrown upon the ‘himself’. We may speak of Our Lord as ‘emptying Himself’ of something else, but scarcely, with this strength of emphasis, of His ‘emptying Himself’ of something else. This emphatic ‘Himself’, interposed between the preceding clause and the verb rendered ‘emptied’, builds a barrier over which we cannot climb backward in search of that of which Our Lord emptied Himself… ‘He made no account of Himself’, we may fairly paraphrase the clause; and thus all question of what He emptied Himself of falls away. What Our Lord actually did, according to Paul, is expressed in the following clauses; those not before us express more the moral character of His act. He took ‘the form of a servant’, and so was ‘made in the likeness of men’.
Bruce Milne