Consider the definition of "acknowledge" in Philippians 2:11.Paul was speaking there of all acknowledging what is actually true, when going before the Lord in the Judgement. At which point, "some" as the scriptures also say rise up to everlasting life, but also "some to everlasting contempt" (meaning an eternal continuance of separation from God based on their own contempt).
Which is not to say that God has not take mercy on "all", but that all have not received it by their own evil. In this way, darkness is not "saved", but rejected and eliminated, by the same measure, by choice.
Note on "acknowledge" in Philippians 2:11 from Strong's Concordance
S1843 eksomologéō (from 1537 /ek, "wholly out from," intensifying 3670 /homologéō, "say the same thing about") – properly, fully agree and to acknowledge that agreement openly (whole-heartedly); hence, to confess ("openly declare"), without reservation (no holding back).
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