Jesus Christ is not just the hinge of history, separating all of history into before and after His birth. Who you understand Jesus Christ to be is what separates Christianity from every other faith.
The apostle John writing in 1 John 2:18-29 is fortifying the church from false teachings that were threatening to undermine the apostolic doctrines of the church regarding who Jesus was.
John makes some quite clear statements that draw a line between what is Christian and what is ‘against God’ (antichrist).
“Who is the liar but he who denies that Jesus is the Christ? This is the antichrist, he who denies the Father and the Son.” (1 John 2:22)
John, as usual, is making stark contrasts. Those he is writing to know ‘the truth’ (vs21) while the person who denies Jesus’ divinity is ‘the liar.’ Such a person is not just wrong but anti-God, against God.
John is saying that; “everything depends on what a person believes about Jesus Christ. If an individual does not believe that Jesus of Nazareth was and is the Christ, God’s own Son, sent from the Father, then he is (literally) against Christ.” (David Jackman)
More than this, we see from vs23 that the Trinity is not divisible. The Father, the Son and the Spirit can not be separated, to deny the Son is to deny the Father and conversely accepting the Son causes one to be in a state of right relationship with the Father also!
Who is Jesus Christ? This is essentially the BIG QUESTION that every person on the planet has to answer, and it is also the most important test, that sorts out all religious teaching we may hear.
John confirms that the teaching about Jesus from the very beginning has not changed (vs24-25). It will not change, does not need updating but believing in the Gospel truth about Jesus comes with an amazing promise – eternal life.
So, remain in Jesus. Stand firm against all notions that divert from the truth portrayed in the Gospels about Jesus. Remain, believing in Jesus Christ so that when He appears in glory, you’ll be excited to see Him and not shrinking back because you diverted from the truth (vs26-28).
In closing, the church wrestled with false teaching about who Jesus was for nearly three hundred years after this letter was written by John. Which is not surprising since the enemy must have tried everything in his power to derail God’s church.
Finally, in 451AD the Fathers of the church from the known world agreed on this long but important statement of faith/creed about who Jesus is for us as Christ Followers. This statement has never been updated and has never needed to be nor will it never need to be;
Chalcedonian Creed from the Council of Chalcedon 451
“We, then, following the holy Fathers, all with one consent, teach men to confess one and the same Son, our Lord Jesus Christ, the same perfect in Godhead and also perfect in manhood; truly God and truly man, of a reasonable [rational] soul and body; consubstantial [co-essential] with the Father according to the Godhead, and consubstantial with us according to the Manhood; in all things like unto us, without sin; begotten before all ages of the Father according to the Godhead, and in these latter days, for us and for our salvation, born of the Virgin Mary, the Mother of God, according to the Manhood; one and the same Christ, Son, Lord, only begotten, to be acknowledged in two natures, inconfusedly, unchangeably, indivisibly, inseparably; the distinction of natures being by no means taken away by the union, but rather the property of each nature being preserved, and concurring in one Person and one Subsistence, not parted or divided into two persons, but one and the same Son, and only begotten, God the Word, the Lord Jesus Christ; as the prophets from the beginning [have declared] concerning Him, and the Lord Jesus Christ Himself has taught us, and the Creed of the holy Fathers has handed down to us.”
Chew on that for a while, marvel at Jesus and worship Him!