John 7:17 (ESV) … “If anyone’s will is to do God’s will, he will know whether the teaching is from God or whether I am speaking on my own authority.”
Everyone’s teaching stands or falls by the fruit it produces in the lives of those who embrace it.
Take for instance the theory of evolution, propounded by Charles Darwin, popularized by T. H. Huxley, and accepted as true today by millions. Let us put it to this test. “If any will embrace it and translate it into action, he shall know of the doctrine, whether it be of God.” When reduced to its lowest common multiple, the theory of evolution applauds the survival of the fittest. It is the theory that might is right. Away with the weak, the infirm, the deformed. Let the law of the jungle hold sway. It is the theory that underlies many of the social and political philosophies of our time. Hitler embraced it. It is at the heart of Nazi philosophy. The theory of a master race, “blitzkrieging” across Europe eradicating the despised of the human family (Jews, Slavs, blacks, gypsies), draws its inspiration from the theory of evolution.
Hitler reveled in the vision of magnificent blonde Aryans, armed and uniformed, striding in jack boots on the bodies of the slain. Behind the panzer divisions, the U-boat wolf packs, the Luftwaffe, was the philosophy of Nazism. Behind the political philosophy of Nazism with its Gestapo, concentration camps, and gas chambers was the theory of evolution. Behind Marx and Lenin and communism is the theory of evolution. Behind secular humanism with its attack on Christian morality is the theory of evolution. No matter how the theory may be bolstered by those brainwashed by our colleges and universities, the theory stands condemned by its fruits.
“Put my teaching to the test,” Jesus challenged his listeners. And that is the answer to those who say that Christianity has failed. Here and there a man, a woman, a teenager, a boy, a girl, dares to stake all on Christ. What happens? It works. The Lord’s teaching, when put to the test, makes the drunken sober, the profligate pure, and the crooked straight. It cleanses society, redeems the individual, transforms lives, makes people godly and Christ-like. That claim can be made by no other philosophy, theory, or religion on earth.
 Phillips, J. (2009). Exploring the Gospel of John: An Expository Commentary (Jn 7:16–18). Kregel Publications; WORDsearch Corp.