If you would help me with a question on the subject of the Devil, I would be grateful to you. If evil comes from within, as stated in Mark 7:18-23 and James 1:14-15, what difference does it make if there is a real devil or not?
If you are willing to accept God's statements in Mark and James concerning the root cause of sin, why do you doubt the same Bible that states, "Be sober, be vigilant; because your adversary the devil walks about like a roaring lion, seeking whom he may devour" (I Peter 5:8). Or are you stating that Jesus didn't understand when he stated, "You are of your father the devil, and the desires of your father you want to do. He was a murderer from the beginning, and does not stand in the truth, because there is no truth in him. When he speaks a lie, he speaks from his own resources, for he is a liar and the father of it" (John 8:44). Or who was it that Jesus faced in the wilderness and debated (Matthew 4; Luke 4)?
The question is not whether the Devil is real or not. In the Bible it is a simple fact. But in the question of responsibility for sin, we cannot shift the blame for our choices on to the one who encouraged us to sin.
Satan cannot make a person sin. That is why it is strongly stated that no one can remove us from God. "My sheep hear My voice, and I know them, and they follow Me. And I give them eternal life, and they shall never perish; neither shall anyone snatch them out of My hand. My Father, who has given them to Me, is greater than all; and no one is able to snatch them out of My Father's hand" (John 10:27-29). Yet, what is not said is that a person cannot choose to leave.
The Devil has set himself against God. He wants to destroy the work of God and he does so by using the desires of people to lure them away from God and into sin. James 1:13-16 documents the progression of sin. Notice "But each one is tempted when he is drawn away by his own desires and enticed" (James 1:14). James is not saying that a person's desires tempt him, but that temptation uses a person's desires against the person. James states that God is not the source of that temptation (James 1:13), but he doesn't state that there is no external source. Later on James states, "Therefore submit to God. Resist the devil and he will flee from you" (James 4:7).
In Mark 7:18-23, Jesus is dealing with the concept of uncleanness or defiling. The Jews had decided that defilement was solely an external matter. You touched something and you became unclean. Jesus points out that it is lust (evil desire) that makes a person unclean. Again Satan can't make a person defiled. But he does encourage a person to defile himself by encouraging him to lust after forbidden things. It is not the temptation that defiles a man, but when a person wants what is being offered, then he defiles his spirit.
As with James, Mark records that Satan is involved in leading men astray. "And these are the ones by the wayside where the word is sown. When they hear, Satan comes immediately and takes away the word that was sown in their hearts" (Mark 4:15). But even with Satan's involvement, we are left without an excuse when we take the lure. Satan uses our desires, our appetites against us, but it is we who take what is offered under strong consideration and then chose to bite the hook.