According to Paul in Romans 8:2 there are two laws that govern human life and well being – “the law of sin and death” and “the law of the Spirit,” and it’s either one or the other that we are controlled by (verses 8-9).
Another way of describing the law of sin and death is the law of “the sinful nature” (verse 3), because it operates just like a law too: “live according to the sinful nature,” Paul writes in verse 5, and automatically, just like a law, we “have our minds set on what that nature desires.” But “those who live in accordance with the Spirit have their minds set” – just like a law again – “on what the Spirit desires.” Two laws in action, that automatically control what goes on inside our heads.
The difference for Christians is that we “are controlled not by the sinful nature but by the Spirit,” verse 9, and when we’re controlled by the Spirit a law is now operating in our heads that enables us, at last, “to put to death the misdeeds of the body,” verse 13. This is “the law of the Spirit.”
The Spirit is committed to setting us free (verse 2) by gently and relentlessly transforming our natural instincts and ungodly desires into the nature and desires that Christ has. That’s why the Spirit is also called “the Spirit of Christ” (verse 9), because it’s Christ’s nature that the Spirit is gradually installing in our heads, replacing our sinful nature – and the Spirit will keep on installing Christ’s nature in our heads even when we’re too weak to care. That’s when the Spirit sighs on our behalf (verse 26), to get us back on the road to “life and peace” (verse 6), brimming with confidence and peace of mind again as we find ourselves able and willing to “please God” (verse 8) instead of being “hostile” to him (verse 7).
Fortunately, the Spirit knows exactly what God put in human heads when he created us, so while we’re helplessly unable to be what God meant us to be, the Spirit is carting off the accumulated rubbish that’s been blocking all those lovely desires and longings God tucked away inside our heads in the beginning when he made us in his image.
And like a law, again, there isn’t a time in our lives, or a situation we come up against, that can stop the Spirit working it out for our good (verse 28). He is constantly and faithfully digging away inside our heads creating the same unclogged, smoothly running, freely purring motor that powers Jesus, because “the Spirit of him who raised Jesus from the dead is (now) living in you,” verse 11.