All Christians should be biblically familiar with the real meaning of what most call “Christmas”, which is the most important event in all of human history: God became flesh. It is a celebration of God the Son adding a new nature and becoming flesh, in order to live the perfect life and die on the cross fulfilling the requirements of God’s perfect and holy justice. This produced both forgiveness of our sins and the evasion of divine wrath that was due to us because of sin (cf. 2 Cor. 5:21; Gal. 3:13). The fact that the eternal Word, Jesus Christ, stepped into His own creation to provide redemption for sinners is the theological trademark and faith to which true Christians are devoted.
Essential Part of the Gospel
The perpetual incarnation of God the Son is one of the most essential and foundational doctrines of Christendom – not only does it define true Christianity, but it defines the work of the Son—the gospel itself! The Incarnation is fully revealed in the NT. Paul calls it a “mystery” meaning that it was once hidden (pre-NT), but now has been revealed (NT). However, we do see allusions of it in the OT (cf. Isa. 9:6: “child[humanity] will be born to us, a son [deity] will be given to us”). The Apostle Paul says in 2 Timothy 2:8: “Remember Jesus Christ, risen from the dead, descendant of David, according to my gospel.” The term translated “descendant” is from the Greek spermatos (from sperma), which means that He was from the literal bloodline of David, nothing metaphorical or figurative about it—God actually became flesh (cf. Rom. 9:5). Only as God-man could Paul say that is was the “Lord of glory” that was crucified (1 Cor. 2:8; cf. 1 Sam. 15:29; Acts 7:1), or say in his farewell address to the elders/overseers (pastors) of the church of Ephesus: “the Holy Spirit has made you overseers, to shepherd the church of God which He purchased with His own blood (Acts 20:28). God’s “own blood” is the blood of the God-man, Jesus Christ(Acts 20:28).
JOHN 1:1 (trans. mine): In the beginning before time, the Word was (ēn) already existing [eternally, cf. Phil. 2:6], and the Word was with [pros], distinctly and intimately, God [the Father], and the Word as to His essential nature/essence [i.e., qualitatively] was fully God [theos—in the same sense, but not the same person as that of God the Father].” Two distinct persons sharing the same nature of God.
JOHN 1:14 (trans. mine): And the Word [who was God] became flesh and tabernacled among us, and we saw His glory, glory as of the one and only, unique one, from the Father, full of grace and truth.” The verb eskēnōsen (“dwelt among us,” NASB) derives its meaning from the Hebrew term sākan referring to Yahweh coming down to earth to dwell (cf. Exod. 25:8; cf. 2 Sam. 7:5-6). In verse 1, the Apostle John positively affirmed that the Word was (a) eternal/preexistent (1:1a), (b) distinct from God the Father (1:1b), and (c) absolutely God (1:1c). In verse 14, John further identifies the bodily incarnation of God the eternal Word showing that Jesus Christ was not merely a temporary “theophany” (theos + phainō, lit., “God appearance”; e.g., Gen. chaps. 18-19), but rather “the Word became flesh [ho logos sarx egeneto].” The Greek here clearly indicates that God the Son did not “wrap” Himself in flesh as one would put on an outfit or costume, but He actually BECAME (egeneto) flesh.
JOHN 1:18: “No one has seen God [the Father] at any time; the only begotten God who is [ho ōn] in the bosom of the Father, He has explained Him.” The prologue of John (vv. 1-18) contains some of the highest Christology in the NT (as does the prologues of Col. and Heb.). After having established the Word’s deity (including His role as the Creator), preexistence, distinction from the Father, and His incarnation, now in verse 18, the perpetual incarnation of the eternal Word is expressed. The phrase (“who is”) present active articular participle ho ōn (“who is,” lit., “the one being”) denoting timeless ongoing existence (as with Rom. 9:5: “Christ according to the flesh, who is [ho ōn, i.e., “the one who is/being always”] over all, God blessed forever. Amen.”
Systematic theologian, Robert Reymond remarks on the significance of the articular participle: “The present participle ho ōn . . . indicates a continuing state of being: ‘who is continually in the bosom of the Father’” (Reymond, Systematic Theology) In the LXX of Exodus 3:14, we find the same articular participle denoting Yahweh’s eternal existence: Egō eimi ho ōn, literally, “I am the eternal/always existing One.” Thus, “No one has seen God at any time; the only begotten God who is [ho ōn, i.e., “the one who is/being always”] in the bosom of the Father, He has explained [“exegeted”] Him.”
PHILIPPIANS 2:7: He “emptied Himself, taking the form of a servant, and being made in the likeness of men.” Verse 6 starts with the affirmation that Christ is “always existing” in the form/nature of God (as clearly taught in John 1:1, 5:17-18; Titus 2:13; Rev. 1:8, 22:13 et al). However, He “did not regard equality with God a thing to be grasped,” that is, to be used for His own independent advantage. “But [He Himself] emptied Himself, taking the form of a bond-servant, and being made in the likeness of men. Being found in appearance as a man, He humbled Himself by becoming obedient to the point of death, even death on a cross”— God the Son emptied Himself by incarnating Himself in order to provide definite redemption by His vicarious and perfect life and substitutionary death on the cross.
The Necessity of God Becoming Man
First, no “mere man” can provide redemption (cf. Ps. 49:7-8), but as perfect man and fully God, Jesus’ redemptive work has infinite value, as He declared on the cross, “It is finished”! Second, as perfect man,Christ lived the perfect life fulfilling the “covenant of works” that Adam did not keep and to which all humans are related (cf. Gen. 2:17; Hosea 6:7; Rom. 5:5-13). God required perfect obedience, which resulted in the promise of eternal life. Adam, as well as all humans, could not keep this covenant. So, God enacted a new covenant, a covenant of grace, in which salvation is granted to sinners, but not on grounds of their own merits, rather the merits of the incarnate “God Christ,” the “second Adam,” who met all the requirements of the justice of God in not only His vicarious cross work, but also His perfect and substitutionary life. That is why Paul says that we “shall be saved by His life” (Rom. 5:10).
Hence, the incarnation of God the Son was the very means God provided to redeem His people—“the Word became flesh and dwelled among us.” Only because the Son is both God and man is He now our Priest in which He intercedes (mediates) forever between God the Father and us (cf. 1 Tim. 2:5; Heb. 7:24-25).
The Perpetual Incarnation
The incarnation of the second person of the Trinity, God the Son, was not a temporary event, rather it was perpetual and is permanent—He is forever more God in the flesh.
COLOSSIANS 2:9:“For in Him all the fullness of Deity dwells in bodily form.” The book of Colossians sharply refutes the dualistic ideology (i.e., spirit vs. matter) of gnostic philosophy that rejected the material/physical world). Some the “Docetic” gnostics went so far as to say it really did not exist—anything physical was illusory only seeming to be real. Hence, they naturally repudiated the concept of Jesus being God in the flesh. Paul opposed this view, definitively presenting the Christ as the Creator of all things and (cf. 1:16-17), and in Him, Christ, presently, continuously, and permanently “dwells” (katoikei) all the fullness (plērōma) of Deity (theotētos) in bodily form (sōmatikōs)—namely, Jesus is God in the flesh. Therefore, against the Gnostics, in 2:9 (and many other places), Paul stresses in the strongest way that in the person of God the Son, Jesus Christ, continuously and permanently dwells all the fullness of God in human flesh.
1 & 2 JOHN. In these two epistles, we find the same problem that Paul addresses in Colossians. The incarnation of Jesus Christ was so essential to the Christian faith that the Apostle John sees it as the ultimate test of true orthodoxy—namely, genuine Christianity. As with Colossians, John provides a sharp refutation against the flesh-denying Gnostics. This is especially seen in 1 John 4:2-3:
By this you know the Spirit of God: every spirit that confesses that Jesus Christ has come in the flesh is from God; 3and every spirit that does not confess Jesus is not from God; this is the spirit of the antichrist.
Note the phrase translated “has come” is from the Greek verb elēluthota, which is a perfect active participle (from erchomai, “to come”). The general import of a perfect tense is a completed action occurring in the past with continuous effects; it denotes a present condition or state resulting from a past action (the perfect is used in John 19:30: “It is [has been for all time] finished.” Thus, the literal reading of verse 2 is “Every spirit that confesses/acknowledges that Jesus Christ has come and remains in the flesh is from God.” The two-natured person, God the Son, became and remains in the flesh. John expresses the same in 2 John 1:7 where the present active participle is used to express the same thing:
For many deceivers have gone out into the world, those who do not acknowledge Jesus Christ as coming [and remaining] in the flesh. This is the deceiver and the antichrist.
The Apostle John sees that believing that Jesus Christ is God in the flesh presently and forevermore is a mark of true Christianity. In fact, so important is this biblical truth to John that anyone who denies it (as with JWs) is not only characterized as “the spirit of the antichrist,” but in 2 John 1:7, this person is ho planos (‘the deceiver”) and ho antichristos (“the antichrist”)—note the definite article precedes both nouns.
Scripture explicitly stresses both the necessity and importance of the incarnation—namely, knowing and understanding that Jesus Christ became man and thus remains the God-man forever (cf. Acts 17:31; 1 Tim. 2:5). Hence, we must always include the incarnation and deity of the Lord Jesus Christ in our proclamation of the gospel, just as biblical authors and the early church did—not merely on December 25th.
Because He became flesh, He is our Prophet, Priest, and King. Scripture presents that God the Son actually substituted Himself on behalf of His people, in their place. His cross work perfectly secured salvation for them. Because He became flesh, His substitutionary atonement did not merely make salvation a possibility for all men, but rather it actually and infallibly saved those for whom He died. Christ’s death removed the wrath from those who were effectually called – both Jews and Gentiles, “men from every tribe and tongue and people and nation” (Rev. 5:9)—only because God the Son became flesh.
 By common confession, great is the mystery of godliness: He [or “God”] who was revealed in the flesh. . . .”
 Here the reflexive pronoun heauton (“Himself”) precedes “emptied” (heauton ekenōsen, lit., “He Himself emptied”), which denotes a “self-emptying.”