I see the sin nature being a corruption of the flesh, being the body. The corrupted body with it's corrupted brain forming a corrupted mind. And that mind bears the imprint of Adam's choice, to seek after knowing good and evil, and finding evil to be inescapable on our own once entered.
When we fail to remain walking in faith, and therefore in grace, we are fallen from grace, back into that knowledge of good and evil, judging ourselves according to whether we break rules, which rules, seeking to draw lines in our behavior, eyes fixed on ourselves.
When we walk in faith we stand in God's grace, the goodness that flows from Him upholds us, and all we need know is whether or not we walk in trust and in love.
If we turn from either of these in any direction, we've turned from the truth of our new life. And the moment we realize that we've turned from trusting God, or turned from loving Him, or others, then we need to return to the mind of Christ, because that IS the mind of the Christ. Faith and love and joy and peace, being gentle, and patient, enduring, having control over ourselves, this is the life the mind of Christ causes our life to be.
Any deviation from these things is a deviation towards the mind of the flesh. Jesus set us free from that in it's entirety. We don't realize, and we forget, and we have a tendency to slip back into all that.
Recognizing, and looking back to God in trust brings us immediately back into walking in the Spirit.
Much love!