To attribute a passive sense to harpagmos appears to be unwarranted. Exploring this issue further before coming to any definite conclusions, however, we will note the exegesis of Moises Silva:
The ambiguous phrase in v. 6, [ouch harpagmon hegesato], has created a literature far more extensive than it probably deserves. In particular, one is impressed by the futility of trying to reach a decision regarding Jesus' preexistence and deity on the basis of whether harpagmon has an active meaning or a passive meaning . . . if one opts for the passive idea, is the nuance positive ("windfall, advantage") or negative ("booty, prize")? Further, if it carries a negative nuance, we must decide whether it speaks of a thing already possessed, which one is tempted to hold on to . . . or a thing not possessed, which one may be tempted to snatch. (Silva 117)
In the end, Silva concludes that a sense of retaining may be the most likely meaning of harpagmos in Philippians 2:6ff. But he is forced to admit that such a conclusion is uncertain and not central to the "hymn" of Philippians 2:6-11 (117). Furthermore, he adds that the few instances of harpagmos outside of Christian literature are all active and not passive (as is the case with harpagma). Consulting Abbott-Smith also reveals that "there is certainly a presumption in favour of the active meaning here" since the apostle does not use the LXX form harpagma. Paul thus speaks of an act of seizing: not a thing seized or a prize (A-S 60).
Though being a firm advocate of Trinitarianism, Greek Professor Daniel B. Wallace also openly admits that while it may be theologically "attractive" to construe harpagmos as having a passive sense (in Phil. 2:6), "it is not satisfactory" (Wallace 634). Wallace convincingly demonstrates that we must interpret the verse in the light of the phrase heauton ekenosen. He concludes that the only translation harmonious with Philippians 2:7 is "a thing to be grasped" (an active meaning for harpagmos). We can thus see that an objective look at the usage of harpagmos in the NT leads one to conclude that harpagmos in Phil 2:6 evidently carries the active meaning of snatching (i.e., a usurpation). This apostolic passage therefore appears to be affirming the fact that Jesus did not aspire to equality with God. To the contrary, completely antithetical to the first Adam, the one who existed en morphe theou contentedly subjected himself to his Father in heaven: "What Christ emptied himself of was his right to be served, his privileged position as the Son of God, and his visible glory [morphe] by taking the form of a slave" (Wannamaker 188).