John is talking about antichrists. People who were going to the church, and professed Christ, but now, have professed unbelief in Christ.
I think it speaks for all time because of what John said.
1. If they had been truly of us, they would never have left. This is like other aspects of scripture which says the same, Like a dog returns to his vomit, A person who is really not saved can only act for so long..
2. They (the ones who now do not believe) left to reveal their true self (they they were never saved to begin with (of us)
besides this, I would ask the same question I always ask.
How can someone who is BORN OF GOD, Is CHASTENED BY GOD, has WITNESS and EXPERIENCED his TRUE LOVE because they had FAITH IN GOD.
ever turn from that and stop believing. What reason would God give them to do this? people do not do things without a reason. People deny God because of a reaon,, What reason did God give then that he was not trustworthy?