"O Lord, you have searched me and you know me. You know when I sit and when I rise; you perceive my thoughts from afar, you discern my going out and my lying down, you are familiar with all my ways." (Psalm 139:1-3)
God does indeed know all of our thoughts- even our unconscious thoughts of which we are not fully aware. He knows our intentions, motives and feelings. The danger lies in not realizing this as a fact.
"For the Lord searches all hearts and understands all the imaginations of the thoughts." (Chron. 28:9)
"Would not God have discovered it, since he knows the secrets of the heart?" (Psalms 44:21)
The intent is what God reads from our thoughts. Our intentions are the secrets of the heart. Situations such as when a person gives you what appears to be a gift from the heart, but is actually a ploy to win your favor for self gain.
We cannot know the mind of another, but nothing is hidden from God. He knows every thought and intent.
"And behold, certain of the scribes said within themselves, "This man blasphemes!" And Jesus, knowing their thoughts" (Matt.9:3)
"God looks to see what is in people's hearts." (Romans 8:27)
That is why we should carefully guard our mind because even though Satan cannot read our thoughts, he has the ability to influence them. When we find ourselves thinking and feeling things we know are wrong, we should quickly push those thoughts and feelings away. "Resist the devil, and he will flee from you." (James 4:7)
Unlike God, Satan and his angels don't know everything; they have to figure it out. Satan is very good at summing us up, but he has a problem trying to keep up with the Almighty.
"But we speak the wisdom of God in a mystery, even the hidden wisdom. Which none of the princes of this world knew: for had they known it, they would not have crucified the Lord of glory." ( 1Co 2:7)
Studying the scriptures floods our minds with God's word, which renews our spirit and helps us to conform to the image and mind of Christ.
"Let us hold fast our confession." (Heb 4:14) Or, in other words, to think and speak the words of our Lord. Angels hear them and act on them.
"My sheep hear My voice, and I know them, and they follow Me." (John 10:27)
Whose voice are you hearing, God's or Satan's? Whose words are you speaking?
God's words activate angels. Satan's words activate demons.
Before Saint Peter was filled with the Holly Spirit, he listened to Satan's words and then he spoke them.
"From that time on Jesus began to explain to His disciples that He must go to Jerusalem and suffer many things at the hands of the elders, chief priests and teachers of the law, and that He must be killed and on the third day be raised to life. Peter took Him aside and began to rebuke Him. "Never, Lord!" he said. "This shall never happen to you!" Jesus turned and said to Peter, "Get behind me, Satan! You are a stumbling block to me; you do not have in mind the things of God, but the things of men." (Matthew 16:21)
Are you hearing the voice of God or is Satan influencing you? This is the real danger.
"... be strong in the Lord... that ye may be able to stand against the wiles of the devil. For we wrestle not against flesh and blood, but against principalities, against powers, against the rulers of the darkness of this world, against spiritual wickedness in high places." (Eph. 6:12)
God really does know all of our thoughts, and Satan is an expert at guessing what we are thinking and feeling; which gives him the opportunity to greatly influence us. Therefore, guard your thoughts carefully. If bad thoughts creep into your mind, get rid of them. Praising the Lord will certainly drive Satan away.