To me, if I take this passage all by itself, it is a very difficult passage of scripture to wrap my head around. It has some aspects to it that you normally do not find within the trilogy books of John - it is one of those verses that just goes so far beyond the rest of what is contained within these three amazing minor books.
In context of the other verses around it it has great understanding - but tonight I want to take it all by itself, without reading any of the verses before and after it (and I do not remember them off the top of my head) so this could get totally off-the-wall and totally out-of-context... forgive me if it does.
"if the anointing which you have received" -- this to me speaks about the fact that God gives every single one of His children an anointing. It does not say "which some of you have received", nor does it say that it is a gift like what we see in Romans 12:6-8, 1 Corinthians 12:8-10, 1 Corinthians 12:28, Ephesians 4:11, and 1 Peter 4:11. It is something that all of us have, as a result of being a child of God.
"need no one to teach you" - This is one of those times where the Peshitta translation is hard to understand (along with the ESV and JKV and a few others) because of their uses of the English comma and periods and such. The NIV and Aramaic Bible in Plain English make this section of the verse much more understandable, in that they term it this way "and you have no need that anyone should teach you" - and the Aramaic Bible in Plain English does it the best justice by not putting a period after that bit of text, but rather a comma (,) so it reads much more like the original language, which actually does help make sense of this. What I get from all of this is that because you have the anointing within you there are heavenly things that you simply become aware of on a spiritual depth, because you are that child of God. Sort of like what I mentioned in yesterdays daily bible verse, that the scales over your eyes are opened - only in this case it is more of your heart of stone becoming a heart of flesh, because the anointing an entered into your being and given you the knowledge to know and understand.
"that same anointing which is of God will teach you all things" -- ah this is a good one. This is saying that just because you have the anointing with you, it does not mean you just automatically "know it all". There are aspects of the mysteries of God that you can only learn by spending greater and greater amount of times with God. Just as you learn more throughout your life as a human being, so too does spending greater amounts of time with your Creator result in greater knowledge of Him, because you have invested the time. Yes, you can become a child of God and call it good, but this section of the verse seems to really indicate that if you really want to get to know Him, you have to be a willing student!
"even as I have taught you, abide in it" -- Ah, but here is the part a lot of people do not like. You see, it is not just God that does the teaching... it is your fellow Christians that you need to be learning from as well. Here we see that there was a human teacher, who had taught the ways of God in the ways that only man can. So while there are things that God will teach you by you spending time with Him, you also need to spend time being taught by members of the clergy.