1 John 1:5
 This is the message we have heard from him and proclaim to you, that God is light, and in him is no darkness at all. (ESV)
There seems to always be someone who claims that they have a new word, a new truth, a new theology. Somehow, whatever was believed in the past was inferior to what we now know. While there are aspects of new methods and styles that can be employed in helpful ways the one thing about Biblical truth is that it is unchanging. Do we need a new theology? No. We actually need to follow what the Bible has always said.
 Jesus Christ is the same yesterday and today and forever. (ESV)
The Apostle John is writing this epistle as an old man. After Paul's teaching helped to liberate the church from the Law, now the Apostle John writes to liberate the church from the false teaching of Gnostic heretics. It did not take long for people to infiltrate the church that promoted a new word, a new truth, a new theology. The problem was it was falsehood. One of the primary purposes of 1 John is to counter the false teaching of the Gnostics.
"Gnosticism, influenced by such philosophers as Plato, advocated a dualism asserting that matter was inherently evil and spirit was good. As a result of this presupposition, these false teachers, although attributing some form of deity to Christ, denied his true humanity to preserve Him from evil. It also claimed elevated knowledge, a higher truth known only to those in on the deep things. Only the initiated had the mystical knowledge of truth that was higher even than the Scripture."
- Dr. John MacArthur, www.gty.org
The Gnostics, claimed to be the truly "enlightened" ones. John writes that God is light and in him there is no darkness at all. This speaks to the fact that you cannot dilute or change the truth of God and still have true light. God alone is light. Those who claim special light outside of what God has revealed are in fact walking in darkness.
When you hear a teacher, or read a book, or even think of things in your head, make sure that they come from the only true light, God. You will know it is from him if it lines up with what the Bible says.