R
John was telling his disciples that they didn't need the gnostic teachers in their midst teaching them that they needed a secret knowledge to be saved because they already had been taught the correct saving doctrine of Christ and had the anointing of the spirit of truth to walk in it. That whole epistle is a refutation of the gnostic heresy that was threatening to destroy the church with insidious false doctrines. The only way to know a false doctrine is to have the right one. The spirit alone doesn't cut it.
This ability has meaning because in the old covenant the people of God were at the mercy of the leadership of Israel to tell them what was true and what was not. In this New Covenant the people of God have the anointing in themselves to tell them if what they are being told is truth or not. We do not need someone to tell us what we are hearing is truth or not. We know that by the Holy Spirit within.
"These things I have written to you concerning those who are trying to deceive you. 27As for you, the anointing which you received from Him abides in you, and you have no need for anyone to teach you"-1 John 2:26-27