Adam Clarke on 1 John 2:3

And hereby we do know that we know him - If we keep the commandments of God, loving him with all our heart, and our neighbor as ourselves, we have the fullest proof that we have the true saving knowledge of God and his Christ. The Gnostics pretended to much knowledge, but their knowledge left them in possession of all their bad passions and unholy habits; they, therefore, gave no proof that they had known either God or his Son Jesus - nor is any man properly acquainted with God, who is still under the power of his sins.