Q: Can the demons communicate anything good? And how does one discover that it is demonic? And what distinguishes it from something good from God?
A: To someone it might seem that he receives something good, but this is from the evil one for his deception. For every good thing which comes from the devil for the deception of a man, being precisely examined, turns out to be unreal; for the devil is a liar, and there is no truth in him (John 8:44), as is shown by the consequences of that (false good). His light ends in darkness, according to the Apostle’s word which speaks about diabolic heralds transformed into the servants of righteousness "whose end will be according to their deeds" (II Corinthians 11:15); and the Savior says: "By their fruit ye shall know them" (Matthew 7:16). If you investigate with understanding and judgment, you will find in the false good (which comes) from the devil, there was not even a trace of good, but either vainglory, or disturbance, or something similar; but the good which comes from God always increases enlightenment and humility of heart and gives a man quietness. But when, out of ignorance, we suffer in something from the deception of the evil one, and later we recognize in this a temptation, then let us call ourselves and hasten to Him Who is powerful to do away with this temptation. One should know that to some the difference (between the good of the devil and that of God) is understandable from the very beginning; while to sinners, only at the end (of the temptation), just as a skilled master in gold work can take gold (in his hand) and tell before it is tested with fire of what sort it is, while an unskilled one does not find this out until it has been tested with fire.