1. II. Light and Darkness (1:5-2:24)
    1. D. Test of Truth (2:18-2:24)
      1. i. Danger of false teachers and Antichrist (2:18-2:19)

Calvin

2:18
Not only are the faithful warned against deceptive teachings, but they are encouraged to be awakened by these deceptions to the realization that Christ's return is soon. The 'last times' John points to are the times when nothing remains to be done except for Christ to return. As such, he was not being misleading in declaring that time to be soon - and in the scheme of God's eternity, even the millennia since John's writing are short. It is clear that the church had been taught from the start that disorder would come to test them, and that such teaching was meant to continue to safeguard all to come. We need to remember that not only is antichrist's appearance spoken of in Scripture, but also his distinguishing characteristics, that we be not blinded by him at his coming. Antichrist is not a single person, but a body of people led by the adversary. (2Th 2:3-4 - apostasy [suggesting a multiplicity of apostates] must occur, led by the adversary who attempts to set himself up as God.) Those whom John refers to are sects that were as forerunners to the future antichrist. Antichrist himself was not yet present, but the mystery of iniquity was already at work. What the Spirit warned of then, so close to the beginning, is even more of a warning to us who stand closer to the end - when Christ is held in dishonor even amongst portions of the Church. [Truer today than even in Calvin's time.]
2:19
That the apostates came from within was even more disturbing than had they been external foes. But John points out that the Church is always thus exposed to charlatanry, thus the need to be on guard to know the truth. Though they had claimed a place in the number of the saved, they were not saved. (2Ti 2:19 - God's seal is pure, because He knows who are His.) How then to explain the backslid? Three types profess: a) those who profess falsely, even as conscience reproves them, b) those who testify falsely even to themselves, futilely convincing themselves of their own righteousness as they disobey, and c) those with living faith, the testimony of their adoption firm in their hearts. These last cannot be disturbed from the Church for they are the Church. God is constant, and so then is His election. Those who fall away must needs be from the first two categories - never truly filled with His knowledge, but only tasting it as with the tip of their tongue. Trial must come to the Church, that it might be cleansed of the chaff.
 
 

Matthew Henry

2:18-2:19
The warning is to all, not just the youngest class of Christian. The order of things as they are known is ending, including the Mosaic institutions, the Hebrew sanctuary, et al. (Da 9:26 - Messiah is cut off after 62 weeks [how does this fit the weeks = years crowd?], the end coming in flood and war.) Antichrists come - within God's providence - but His people are warned, and His house protected by His watchmen. The Church having been warned of Messiah's great adversary shouldn't be surprised at the numerous lesser forerunners. (2Th 2:8-10 - Antichrist must come, not Satan but one in accord with him - and must be defeated by Christ's appearing.) Even these lesser ones were foretold by Christ Himself. (Mt 24:24 - false Christs come to deceive by signs and wonders.) Knowing this, their appearance ought to strengthen faith. These came from within the Church, having claimed to believe its teachings, but not united with Christ. That they weren't what they claimed, is shown in their very apostasy, for true faith would have held them to true doctrine. They were permitted to depart from truth to show their insincerity and - when possible and permissible - to return them to truth. (2Pe 3:17-18 - knowing that some preach falsehood, we ought to be careful not to follow them, but rather to cling to truth and grow in the knowledge that Christ's grace teaches.)
 
 

Adam Clarke

2:18
Some think this passage refers to the end of Israel in the Roman destruction. Others think it written after that destruction, and thus refer it to the perilous endtimes predicted by Jesus. (Mt 7:15 - He warned against the coming of false prophets, Mt 24:11-12 - causing many to lose their love.) Adam stands with the former, believing the letter written before AD 70. The antichrist referred to is not one particular person or sect, but anything in opposition to the Gospel message. This includes attempts to water down that message. Many such heretics come, showing that we are in the time predicted by Christ.
2:19
Such as corrupt or reduce the true message of the Gospel are not acknowledged as Christians by the heads of the Church, there falsity having shown for a time prior to their departure from the Church, else they would not have been forming their own sects. They were neither expelled nor sent out by the Church, but rather separated themselves from the Church, showing themselves to be taught by other than the Holy Spirit. In departing, they perhaps drew some true believers with them for a time.
 
 

Barnes

2:18
John points out the last dispensation, not indicating anything as to its duration. (Isa 2:2 - Isaiah speaks of the last days, Ac 2:17 - More prophecies of the last days dispensation are quoted, Heb 1:2 - The last days began with the preaching of God's Son.) This does not refer to the fall of Jerusalem. Antichrist is a term unique to John's writings, wherein it properly indicates anybody who claimed Christ's place, or was in opposition to Him. Given John's own definitions of who counts as antichrists, he clearly uses the term to denote one who held views in opposition to Christ's own message and doctrine - either denying His very Christhood, or denying His physical presence. Points regarding antichrist: 1) many would claim to be Christ or Messiah (Mt 24:5 - many come saying 'I am Christ', Mt 24:24 - even showing signs and wonders.) 2) the spirit of apostasy would eventually focus on one leader, or succession of leaders as the primary 'spirit of antichrist' (2Th 2:1-7 - a great apostasy must precede the end.) 3) eventually, this focus will be upon the 'man of sin.' 4) Prior to this focussing, many would already be taken in by that spirit. Paul looks to the future concentration in his writings, John looks to the present state as proof that the final dispensation had begun already. John sees many about him opposing the truth of Christ, and thus recognizes that the dispensation is at hand. We can not ascertain the exact group John has in mind, but could conjecture that he refers to Jewish denial of Jesus' divinity, or Docetic denial of His manhood.
2:19
John notes that these false prophets came from within, and were therefor familiar to his readers - i.e. they could easily confirm his impression of the situation. Having become apostate, it is clear they were never true believers. (Mt 7:23 - the lawless were never known of God, despite any claims they may have made to the contrary.) This is essentially a statement of the fact that a true believer cannot fall away, and one who falls away cannot be a true believer. Their apostasy is within God's providence, being desirable in that (a) the church is purified by their departure (Jn 15:2 - fruitless branches are pruned away,) (b) the church might not become responsible for their conduct, (c) they might see their true selves and realize their non-Christianity [presumably then repenting], (d) their teachings would be discounted once their real situation was known, (e) their own delusions might end in repentance. The likelihood of their repentance is much greater once they are removed from their false association and freed from their deceptions. Those who leave religion to live in sin or heresy never had true piety. Their fall proves nothing as to whether a true Christian can fall from grace [it actually tends to say quite the opposite.] A true Christian may backslide, but he will not permanently depart the Church. Our continuance with the true Church - in spirit and truth - is a great evidence of our piety. Those who profess falsely are allowed to apostatize mainly to show themselves and others their true state that others might not be misled, and that they themselves might see and repent.
 
 

Wycliffe

2:18
One with the experience of age addresses all his readers. They enter into the time when trouble and persecution will grow. Antichrist refers to those "who oppose Christ under the guise of Christ." Since such opposers have been with us from John's time to our own, the "last hour" must refer to the period between Jesus' two advents.
2:19
Outwardly, such appeared to be part of the church, but were never part of the body. That they would depart from the body shows that they were never really body parts.
 
 

Jamieson, Fausset & Brown

2:18
Children refers to age, the fathers and young men being gone then. The last time is a period in which the worldly mentioned above will attempt to lure away the pious. Such have ever been a thorn to the church to keep it waiting for its Savior. (1Co 10:11 - what is written is written as an example for us who live in the end.) The apostles had already spoken of these occurrences (2Th 2:3-10, Ac 20:29-30 - wolves from amongst you will come.) Antichrist indicates a false or replacement Christ, or one in opposition to Christ. Good quote here: he "opposeth himself to all that is called God. For God's great truth, 'God is man,' he substitutes his own lie, 'man is God'" - attributed to Trench. The many antichrists noted by John equate to the active mystery of lawlessness noted by Paul (2Th 2:7.) These are not the Antichrist, who is the little horn (Da 7:8, Da 7:20), the man of sin (2Th 2:1-7), the beast from the bottomless pit (Rev 11:7, Rev 17:8), the false prophet, the second beast (Rev 13:3, Rev 13:11-18, Rev 16:13).
2:19
That they have gone out does not necessarily mean that they have declared their departure, only that they are no longer in the truth. They are not within the spiritual fellowship. The elect cannot fall. This isn't fate, but the necessity of the self. Either we are in Christ, or antichrist, there is no middle ground. The verse implies that some antichrists are of us, or that all who are among us are not necessarily of us. (1Co 11:19 - the appearance of factions in the church serves to show which are true and which are not.)
 
 

New Thoughts

It's interesting, looking back on my previous thoughts, to see that what appears a great evil to the eye, serves a great and good purpose in God's view. That a false teacher might lead many astray is true, but for the most part, those led astray were already straying of their own accord. The exceptions are still held by God's grace, and will be returned chastened, purified, and renewed. Meanwhile, that which is false and harmful is successfully removed from the church body, leaving it healthier, and better equipped to go on. It's also interesting to see this situation defining the 'end times'. That it extends so far should, perhaps, not be surprising. It does tend to give me more of a sense that we're approaching the end of the end, although I couldn't really say why. Just a feeling, a sense. The re-assurances offered are welcome, as well. That God continues to hold His own in His hands - in spite of any foolish side-tracks they might take. That is welcome news indeed! Lord, I thank You that You are so patient with us, that You are so constant with us. I am blessed to know Your grace, and to know Your grace never leaves or forsakes. I am thankful for Your warnings, that keep us prepared for what must come. I am thankful for Your explanations, that what must come seem not frivolous or capricious. Lord, help me - help us - to keep ever in mind that signs and wonders in the end prove nothing, nor does their absence. The proof is in the fruit. Look at our lives. Make us such that we welcome others to look at our lives. The act is nothing, the truth is all. Lord, help us to live out the truth of our beliefs. Burn away all our hypocrisy, purify my heart, make me to stand unashamed and unblemished as a testimony to Your goodness.