Is there a power like Satan that weakens God's influence on the soul?
Satan can call people towards evil, but he has no power to break God's work within the soul. Whoever follows him chooses to do so and thereby turns away from God.
The question begins with a beautiful thought. The deepest layer of the human soul can be reached only by God. No teacher, no friend and no upbringing gets that far. The first verse above says that God is nearer to man than his own jugular vein and knows what his soul whispers to him.
The Holy Qur’an also speaks of Satan. Yet it does not describe him as a second power wrestling with God on equal terms for the soul. Satan can tempt, make promises and call towards evil. He cannot force anyone. In the second verse he admits in the end that he had no authority. He only called, and people followed him.
This places the responsibility with man. God's influence reaches every soul, but a person can close himself off from it. Someone who gives in to the call of evil again and again grows numb to the voice within. God's influence has not become weaker. The person has simply turned away and stopped listening.
This teaching does not contradict reason. It explains why people know what is good and still do what is wrong, without taking away their responsibility for what they do. Here revelation and reason walk the same path.
That is why the message of the Holy Qur’an is ultimately a comforting one. Satan has no power over those who believe and put their trust in their Lord. Trust in God is the best protection. Whoever holds on to Him stays open to His work, even when temptation calls loudly.