Bill Tharp, in his article on interpretation, offered an interpretation of I John 2:27 that seemed to skirt the issue.
My speciality in Midrash, I believe, may shed light on this passage. Much of the New Testament, I believe, is Midrash (commentary, explanation, elaboration) on Old Testament passages. I believe I John 2:27 is a Midrash on Jeremiah 31:34 (ESV)
And no longer shall each one teach his neighbor and each his brother, saying, ‘Know the Lord,’ for they shall all know me, from the least of them to the greatest, declares the Lord. For I will forgive their iniquity, and I will remember their sin no more.”
Notice how similar I John 2:27 is:
But the anointing that you received from him abides in you, and you have no need that anyone should teach you. But as his anointing teaches you about everything, and is true, and is no lie—just as it has taught you, abide in him.
Needless to say, Jeremiah 31 is about the New Covenant, and the New Covenant is the age of the Spirit, etc. What makes the "New" Covenant "new," IMO, is not regeneration (which is seen throughout the Old Testament and called "circumcision of the heart)." Rather, it is the fact that Messiah has come, that the Spirit is given, and that only those who know the Lord are under the New Covenant (unlike the Old Covenant, which included the unregenerate).
If I am right, John is saying, "You know everything required to have saving faith (as opposed to Gnostic or false teaching), evidenced by the Spirit who is the hallmark of the New Covenant. "Everything" here parallels 2 Peter 1:3
His divine power has granted to us all things that pertain to life and godliness, through the knowledge of him who called us to his own glory and excellence
By "life," Peter is referring to eternal life, not this life. In other words, the Gospel is enough.