That's the entire fulcrum point of the Gospel. And "whom" we are saved from. Mankind is universally a "slave of Satan" in our minds and hearts, which results in sin.
Here's the shortlist: Mark 4:15, Acts 26:18, 2 Cor. 4:4, 1 John 3:8
The picture of Mark 4:15 and the other seed parables is to show that Satan (and his own) are overlapped
with(in) the heart of mankind. There are in fact TWO parties present within what appears to a flesh sight, only an individual. Paul shows this same scriptural fact upon himself in Romans 7, 2 Cor. 12:7, 1 Tim. 1:15, 2 Tim. 2:20-21. Then lays that identical understanding universally upon mankind in Romans 9 and in every teaching about sin. Paul lays the same understanding upon Israel, specifically again in the beginning of Romans 9, again in Romans 11:8, again in 2 Cor. 3:14. Jesus showed this identical fact in thousands of cases in the Gospel.
In fact this scriptural reality is so entirely obvious, openly revealed and utterly transparently exposed it's nothing less than factual internal blinding in any reader that keeps them from seeing it.
Which CONFIRMS the reality of the blinding and the reality of the Gospel itself.
That I will acknowledge. Satan had nothing "in" Him because He was sinless in thought, Word and Deed. None of us can make that same claim. Jesus tells us that "evil" comes from within, and yes, we all still have that evil infection in our minds. Prior to salvation we didn't know it or see it, that our sin is in fact of the devil who blinds our minds/hearts. After salvation we do see it (or should if we're paying attentions) and are to reign OVER internal temptations and lusts in the flesh, but they are still there, internally,
and they are still sourced to the tempter.
Paul denies that's the case for himself in 2 Cor. 12:7 and in many other citings. John makes the identical case in 1 John 1:8 and 1 John 3:8. Again, I'm only surprised that believers can't pinpoint this matter and are led to "insulate" themselves. I do mean they are "led" in this into denial. The flesh is vile because Satan and his minions through the avenue of temptations and innumerable lusts do have access to our flesh internally, in lusts and temptations.
This is also why the flesh is contrary to the Spirit, because THEY are contrary to the Spirit.
They are what we are "saved" and divided from because we are (at least supposed to) see that temptations are in fact demonic, and we RESIST those things of the DEVIL, internally. We are released from "THEIR" flesh hold by Spiritual Sight. The flesh is actually where their "kingdom" resides. And their power comes from the law, whereby they "enter" man's heart to deceive and to blind.
As it pertains to LAW, the LAW was given precisely to reveal sin, which is of the devil. The devil is also moved into action "in man" where the Word is sown and the LAW is also The Word. That is why no one is technically legal and in fact can't be. Because it's not a question of just a singular person involved with Law.
The tempter is also moved in man, by the law, to resist. The math here is not hard to fathom. Sin is of the devil. The devil resists the law in man. The law therefore gives RESISTING strength to the DEVIL "in man."
In salvation, we, by SIGHT of this internal problem, are called to RESIST our enemies who "tempt" us internally. We are not called to be 'their slave.' But it is blindness to claim that "they" are or can be "legal" in any of us. And that is where legalists go completely off the scriptural rails. The contrariness of the flesh remains with all of us to deal with and to reign over. Gal. 5:17, Romans 6:12, Eph. 6:11-13
1 Corinthians 15:56
The sting of death is sin; and
the strength of sin is the law.
In lying hypocrisy, our minds become "seared shut" to this internal reality. 1 Tim. 4:2