This text from the Letter to the Philippians introduces us into the mystery of Christ's kenosis. To express this mystery the apostle uses first of all the words "emptied himself," which refers especially to the reality of the Incarnation. "The Word became flesh" (Jn 1:14). God the Son assumed human nature, humanity, and became true man, while remaining God! The truth about Christ as man must always be considered in relation to God the Son. This permanent reference itself is indicated by St. Paul's text. "He emptied himself" does not in any way mean that he ceased to be God; that would be absurd! It means rather, as the apostle perceptively expressed it, that "he did not deem equality with God something to be grasped," but "though he was in the form of God" (in forma Dei), as the true Son of God, he assumed a human nature deprived of glory, subject to suffering and death, in which he could live in obedience to the Father, even to the ultimate sacrifice.
Pope John Paul II, "Jesus Christ Emptied Himself", General Audience, Feb 17, 1988