(Just some thoughts)
As a young believer I knew when I met another we would instantly relate to each other regardless of our small theological differences or if we came from different cultures and backgrounds. It was like I saw the spirit inside them and they in me and that made us brothers. It would not matter if I met them before or they spoke another language it was automatic. There was something there that could not be disputed. You would be open to each other and tell each other detail about your lives that you would not with other people you might have met who were not believers.
As time went on this become more difficult. People became more guarded and even though they openly showed affection to you behind your back they would tend betray trust often. This has happened to me in significant ways as people who stood beside me as believers betrayed me in ways I cannot express here but these events broke my spirit. This happened many times which always confused me as I treated them as brothers and could not work out why. So as I got older I trusted other believers less and less because of these experiences which unfortunately increased. This was one of the main contributing factors that lead me to abandon all “Christianity” per se for a number of years. However I did not entirely understand all of the factors.
The reason this internal discussion has arisen specifically is because of so called believers that confess Christ but have are offensive and aggressive stance towards me particularly in recent years. I wondered that if we shared the same core faith how could they consistently attack and harass me. Surely we would become at least friends and have each others back. But that was not the case. In fact certain believers were more friendly towards those in the world than myself which alarmed me during this time of being in a slumber and blaming God for all the previous events that occurred. Recently I have been thankful that God used these people to reprove me however they are still quite offensive towards me to this day. That is their spirit at work and perhaps God will deal with them in time.
Recently I was studying the books John wrote including his Epistles and it hit between my eyes. Not only did it reprove me (John 16: 8And when he is come, he will reproue the world of sinne, and of righteousnesse, and of iudgement.) It also explained what has occurred. What was the spirit behind these attacks on me? Why did people make their attacks personal when it came to relationships with me?
Little children, it is the last time: and as yee haue heard that Antichrist shall come, euen now are there many Antichrists, whereby wee know that it is the last time.
19 They went out from vs, but they were not of vs: for if they had beene of vs, they would no doubt haue continued with vs: but they went out that they might be made manifest, that they were not all of vs.
Before I get in to that I want to take on a word reproue (yes as it appears in the 1611) which corrupt bibles often replace with the word convict. In fact I found the word convict in corrupt bibles 15 times. It is used to replace many words in the original 1611. The most common words used in the 1611 were judge, rebuke and reprove and never convict. Why is that? Could it be that convict is a legal word used in law and this is conditioning for society? I wonder.
With that aside touched on I wanted to explain why seeming brothers betray and turn on you specifically and the word is Antichrist. They have the spirit of Antichrist. They oppose and replace Christ with another spirit. John says they went out from us which means they once were amongst us but if they did not have this spirit they would have remained but they did not. However what if these spirits stayed amongst us in churches? These people would be parading as believers, smiling, hugging cleaning the church buildings but still with the same spirit.
Simply put this would explain why these brothers so vehemently yet subtlety attempted to destroy me. Could they have seen my spirit and been opposed to it but I failed to discern it because I could not believe it were possible? I think it might have been the later and the reason is because this subject of Antichrist is so misunderstood by the vast majority of believers. The fact is the testimony used by the modern church has a different spirit itself. The testimony of the false idols (bibles) which of 99% believers use are based on the same spirit of Antichrist. If you need to verify this historical fact there are more than ample resources on this site to get started.
To add to the above I would say that most of these believers never were my brother any more than other people in the world that have even more openly persecuted me where and attempted to make life unpleasant particularly at work which has been the place of constant harassment. This has been even more overt in the past few years. The fact is the spirit of Anti Christ is in the world and people will oppose you even if you never lift an aggressive finger towards them. They will seek you and go out of their way to identify and persecute you. This has been my life long experience and is very discouraging and difficult to deal with especially without the right testimony to be encouraged from. This seems to have culminated in the last few years of history where evil has made an overt and open display. Make no mistake that it was always there as John wrote about it right the beginning of the church. This spirit will oppose you at every opportunity as it is allowed to by God.
That about ends these words for now and was just some thoughts that I wanted to express and see where it lead me. I hope it helped someone or if not at least inspired you to read more on the subject. While we are on this subject I would encourage you to purchase this book that helped me immensely from Reg Block. It is also available in PDF form so please purchase it as valuable resource as much of his content is found on this site. (The title image is from this book too.)

Yes the actual meaning is a substitute for Christs Spirit as in Vicar.