Kai theos ēn ho logos. . . . kai ho logos sarx egeneto kai eskēnōsen en hēmin (literally, “and God was the Word…. and the Word flesh became and tabernacle/dwelled among us”; John 1:1c, 14)
We have stressed continually over the years, the key ultimate test for Christian faith is accurate Christology. In other words, genuine Christianity is biblically defined by having an ultimate trust (faith) in and possessing an accurate knowledge of the person, nature, and finished work of the Lord Jesus Christ of biblical revelation (cf. John 17:3). One’s mere “godly” motives and good works do not merit or determine one’s justification before the Lord. Scripture is clear: good/righteous works performed by unregenerate (unsaved) men may seem good before other men, but are in fact “filthy rags” in the eyes of the Lord (cf. Isa. 64:6).
The unsaved man, says Paul, “does not subject itself to the law of God, for it is not even able to do so, and those who are in the flesh cannot [ou dunatai, lit., “no ability”] please God.” They are in a constant state of active rebellion against the Lord in which any works done in “righteousness” do not please God—rather they add to God’s wrath against such persons.
True Christianity, that is, saving faith, consists of believing and trusting in the one true triune God of biblical revelation and the perfect life and atoning cross-work of Jesus Christ as the sole and sufficient means of salvation that God has provided.
Our celebration of Christmas is a celebration of the incarnation of the Lord Jesus. Jesus Christ, God the Son, became flesh in order to live the perfect life and die on the cross fulfilling the requirements of God’s perfect law and justice—on our behalf: “For our sake He made Him to be sin who knew no sin, so that in Him we might become the righteousness of God” (2 Cor. 5:21; cf. Gal. 3:13). The incarnation of the Lord Jesus is the necessary and only means of propitiation (atoning sacrifice). It was His perfect life and proprietary cross-work that fully satisfied the requirements of God’s perfect and holy justice in which produced both forgiveness of our sins and the evasion of divine wrath due our account because of sin:
For what the Law could not do, weak as it was through the flesh, God did: sending His own Son in the likeness of sinful flesh and as an offering for sin, He condemned sin in the flesh, so that the requirement of the Law might be fulfilled in us, who do not walk according to the flesh but according to the Spirit (Rom. 8:3-4).
The necessity of God becoming man is two-fold. First, as the psalmist confirms: “No man can by any means redeem his brother or give to God a ransom for him—for the redemption of his soul is costly” (Ps. 49:7-8). Thus, no “mere man” can provide redemption, but as perfect 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; Rom. 2:20-26; 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—for all humans are covenant breakers. So, God enacted a new covenant, a covenant of grace in which salvation (eternal life) is granted to sinners, but on the basis of the merits of incarnate Christ, the “second Adam,” who lived the perfect obedient life on our behalf and died sacrificially and substitutionally providing the full payment of sin, which we could never pay. Christ met all the requirements of the justice of God in both His perfect life and His death. 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.”
Jesus Christ entirely paid the penalty of sin averting the wrath of God on our behalf (cf. 1 John 2:2).
Apart from the cross-work of Christ, sinners would have to endure the full penalty of sin for themselves. But, “while we were enemies,” says Paul: “we were reconciled to God through the death of His Son, much more, having been reconciled, we shall be saved by His life.” That is why the author of Hebrews can say: [Jesus] continues forever, holds His priesthood permanently. Therefore He is able also to save forever those who draw near to God through Him, since He always lives to make intercession for them (7:24-25). Only because the Son is both God and man is He now our Priest in which He intercedes (mediates) forever between God and us.
The Perpetual Incarnation is Essential to Christian Faith
As briefly shown above, the incarnation of the second person of the Trinity, God the Son, was the very means, which God provided to redeem sinners (cf. John 1:1, 14; Phil. 2-6-11). Thus, the perpetual or permanent incarnation of the Lord Jesus was an essential and immutable part of the gospel. 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). This means that He was from the literal bloodline of David, nothing metaphorical or figurative about it—God actually became flesh. 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 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.” God’s “own blood” is the blood of the God-man, Jesus Christ.
“For in Him all the fullness of Deity dwells in bodily form”
The book of Colossians sharply refuted the dualistic ideology (i.e., spirit vs. matter) of Gnosticism (viz. proto-Gnosticism). The Gnostics rejected the idea that the so-called “supreme God” would ever dwell in (or create) “evil matter” (as with a material world). Hence, they naturally repudiated the concept of Jesus being God in the flesh. Accordingly, Paul definitely states in essence: Jesus is the Creator of all things, for in Him 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, the Christ that Paul preached was fully God and fully man, “a descendent of David,” the crucified the “Lord of glory” in which we as Christians are reconciled “in His fleshly body through [His physical] death” (Col. 1:22, here Paul again emphasizing His real flesh). The Christ that Paul preached was always existing as God and emptied Himself taking the very nature of humanity humbling Himself becoming obedient to the point of death, even death on a cross—the YHWH of Isaiah’s prophecy in 45:23, who glorifies the distinct person of God the Father (cf. Phil. 2:6-11). Therefore, against the Gnostics, in 2:9 (and many other places), Paul stressed in the strongest way possible 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
The incarnation of Jesus Christ was so essential to the Christian faith that the Apostle John sees it as the ultimate test for 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; and every spirit that does not confess Jesus is not from God; this is the spirit of the antichrist”
Note that the phrase translated “has come” is from the Greek verb elēluthota, which is a perfect active participle (from erchomai, “to come”). The 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. 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.”
Jesus Christ, God the Son, became and remains in the flesh (see also 2 John 7). The Apostle John was clear: 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 fact to the Apostle 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”). So in John’s mind, “the antichrist” is anyone who denies that Jesus Christ, God the Son, came and remains in the flesh.
Scripture explicitly stresses both the necessity and importance of the incarnation, that is, knowing and understanding that Jesus Christ, the Son of God, became man and thus remains forever man—the God-man (cf. Acts 17:31; 1 Tim. 2:5). Hence, we must include the incarnation and deity of the Lord Jesus in our private and public proclamation of the gospel, just as biblical authors and the early church did. This is our faith as Christians, “which was once for all handed down to the saints” (Jude 1:3): Jesus Christ, God the Son, the eternal Word, became flesh and took up residence among us in order that through His perfect life (that we could not live) and through His sacrificial cross-work paid the price for sin (propitiating God’s wrath due our account for sin). Christ did this on our behalf—thus, His work was substitutionary.
Therefore, let us remember and proclaim this truth to the world, not only on Christmas, but at all times to the glory of God.
 In John 19:30, the completed/finished work of redemption is brought out by the use of the perfect indicative verb Tetelestai (translated, “It is finished”) denoting grammatically, a perfect past action with continuous results. This means that although His cross-work was completed over 2000 years ago, the atoning and propitiatory results are felt by us today and every sinner who puts their trust in the Son, Christ Jesus, God in the flesh.
 “Lord of glory” was a divine title. In Acts 7:2, Stephen calls God, “The God of glory” (cf. also 1 Sam. 15:29, “Glory of Israel”).
 As seen, 1 & 2 John along with Colossians was a pointed refutation against the *Docetic Gnostics who denied that Jesus became and remains in the flesh. In the same way, Oneness Pentecostals deny that the person of the Son is God who became flesh and continues to remain in the flesh. They hold to a unipersonal concept of God believing that Jesus is both Father/Holy Spirit and “Son” (who became the Son at Bethlehem). Since they believe the “Son” represents merely the humanity of Jesus, but not His deity, the Son, as they teach, is a temporary non-eternal and non-deity “mode” or “office” of Jesus—thus rejecting any idea of a triune God existing in three persons. Thus, Oneness Pentecostals pervert the biblical presentation of the incarnation of God the Son. In contrast to the Oneness notion of the Son, Scripture teaches in the plainest way that the Son is God/YHWH, the unchangeable Creator, and a distinct person from God the Father and the Holy Spirit (cf. Luke 10:21-22; John 1:1, 18; 17:5; Rom. 1:1-3; 9:5; Phil. 2:6-11; Col. 1:14-20; Heb. 1:2-3, 8, 10-12; 1 John 1:-3; Rev. 5:13; etc.).