In this verse the Apostle issues a stern warning! He tells us to be on the alert because error and false propagators are prolific. He says "many false prophets" will be on the scene.
We Christians must reject an easy and widespread indifference to proven wrong. We are to be willing to warily judge in this way: Statements or professions of faith must be held up to the light of Holy Scripture looking for cracks and dark spots of error. We must relentlessly maintain this readiness. And we must remember that when Jesus said "judge not," He was not speaking contrary to such a process or John's instruction in the above text.
It is true that we limited humans must not judge motives (we just don't know what is in the heart of another person) and must also refuse to impose upon others an unrealistic kind of perfectionism which in this lifetime is impossible to attain. And, if the fundamentals of the faith are intact, we readily agree that there are areas of doctrine wherein honest differences exist.The Almighty knows this and is often more patient with us humans than we are with our fellow humans. For instance: In Psalm 103:14 we are told: "...He Himself knows our frame; He is mindful that we are but dust." And, of course, we are 'dirt dust', not gold dust. God knows the limitations of His creatures, especially since sin entered the world. Therefore, we most certainly are not in the position to judge others with a haughty judgmental spirit. And so, Jesus warns us against such. We must not play God. He alone knows all and the Judge stands at the door. He's looking after everything perfectly so.
But, on the other hand, we must judge in this way: Check out all ideas and philosophies, especially those purporting to be Christian doctrine, by holding them up to the all-pervasive searching rays of Holy Scripture. We must reject the practice of judgmentally going after others but at the same time accept the need for judgment or judging in the light of Scripture, it being the very mind of God. So, interpreting Scripture carefully we let them, in effect, do the judging. God has spoken. Here is what He says about this and that. If anything is contrary to His clear Word, it is wrong. Using such Scripture we then proceed to "prove all things" or put them to the test, even as the Bible so instructs.
Yes, this makes for tensions and conflicts but the clash of ideas is the sound of freedom and price of doctrinal purity.
- dick christen