Charles Hodge on Ephesians 4:20

V. 20. But ye have not so learned Christ. That is, your knowledge of Christ has not led you to live as the heathen. As we are said to learn a thing, but never to learn a person, the expression μανθάνειν τὸν Χριστόν, is without example. But as the Scriptures speak of preaching Christ, which does not mean merely to preach his doctrines, but to preach Christ himself, to set him forth as the object of supreme love and confidence, so "to learn Christ" does not mean merely, to learn his doctrines, but to attain the knowledge of Christ as the Son of God, God in our nature, the Holy one of God, the Saviour from sin, whom to know is holiness and life. Any one who has thus learned Christ cannot live in darkness and sin. Such knowledge is in its very nature light. Where it enters, the mind is irradiated, refined, and purified. Nihil ergo de Christo didicit qui nihil vita ab infidelibus differt; neque eninm a mortificatione carnis separari potest Christi cognitio.—CALVIN.