“Wherefore henceforth know we no man after the flesh: yea, though we have known Christ after the flesh, yet now henceforth know we [Him] no more” (2 Corinthians 5:16; KJV; underlining mine).
“So that we henceforth have known no one according to the flesh, and even if we have known Christ according to the flesh, yet now we know Him no more” (2 Corinthians 5:16; YLT; underlining mine).
Some translations render knowing Christ: “after the flesh.” Other translations read: “according to flesh.” One commentator (Calvin, I think) said the term “flesh” includes all external endowments which mankind are accustomed to hold in high esteem; in brief, everything which, apart from regeneration, is reckoned worthy of praise. A key phrase here is, “apart from regeneration.”
To know Christ “according to flesh” is to know Christ as an unregenerate person “knows” Christ (whether religious or irreligious).
For instance, a person who CLAIMS to believe in the true Jesus of 2 Corinthians 4:6 but who ALSO says that they were regenerate while believing in the false christ of 2 Corinthians 11:4, is a person who knows Christ “according to flesh.” This is the person who CLAIMS to believe the true gospel of Romans 1:16-17 but who ALSO says they were regenerated by the false gospel of Galatians 1:8-9. This person began their alleged “new life in Christ” with the accursed false gospel of Galatians 1:8-9 and then later “grew into” the blessed true gospel of Romans 1:16-17 (abusing 2 Peter 3:18 as a pretext for this type of “growing” that ever-learns, but never acknowledges or loves the grace of God in truth).
The person who knows Christ “according to flesh” might be quite skilled in articulating a particular doctrine that is absolutely essential to the gospel — with (at least) this caveat or qualification: that any of the “essential gospel doctrines” being so clearly explained are NOT NECESSARILY doctrines that every single regenerate person without exception believes.
There are men who, depending on the circumstance or time of day, may APPEAR to be boldly and unashamedly preaching Christ crucified. But when they are pressed on the essential nature of the Word of the Cross, it then appears to them as utter foolishness. In other words, if the teaching of Christ crucified be an OPTIONAL gospel doctrine then it is something for, say, a typical tolerant Calvinist to SAVOR; but if Christ crucified is actually preached as an ESSENTIAL gospel doctrine then it becomes to them a cultic or sectarian STUMBLING BLOCK (cf. 1 Corinthians 1:18-24).
It seems that whatever false christ (e.g., Apollinarian, Nestorian, Eutychian, Arian, Arminian, Ritschlian, etc.) happens to be the facinorous “flavor of the month” it is THAT particular false christ that is the presumed “default-position” among allegedly “newly regenerate Christians.” Why is that? Why do so many professing Christians ASSUME that the teaching of 2 Corinthians 4:6 and 2 Corinthians 5:17 PRECLUDE the revelation of the true Christ of Scripture as an immediate and inevitable fruit of resurrecting power of God the Holy Spirit (i.e., regeneration)? Could it be because the simple gospel of the glory of Christ has not dawned on them?
“But if our gospel be hid, it is hid to them that are lost: In whom the god of this world hath blinded the minds of them which believe not, lest the light of the glorious gospel of Christ, who is the image of God, should shine unto them. For we preach not ourselves, but Christ Jesus the Lord; and ourselves your servants for Jesus’ sake. For God, who commanded the light to shine out of darkness, hath shined in our hearts, to [give] the light of the knowledge of the glory of God in the face of Jesus Christ. But we have this treasure in earthen vessels, that the excellency of the power may be of God, and not of us” (2 Corinthians 4:3-7).
“Wherefore henceforth know we no man after the flesh: yea, though we have known Christ after the flesh, yet now henceforth know we [Him] no more. Therefore if any man [be] in Christ, [he is] a new creature: old things are passed away; behold, all things are become new” (2 Corinthians 5:16-17).