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Paul in promoting Grace has the argument leveled at him (6:1) that his preaching was risky and would only open the 'floodgates of evil' among christians. The accusation had punch and he spends the next chapter showing how grace actually worked and by extension why law did not.
He uses 3 pieces of imagery - a tree graft, a change of master to a worn out slave and a new marriage to illustrate this. They all share the language of an IDENTITY change through a new association. "Crucified WITH him" V6 is the tenor of the language.
1. A TREE GRAFT V5 KJV "planted" or grafted as it can be translated draws on the imagery of an old style tree been given a new lease of life by a grafting in of a stronger cultivar. The tree's whole identity changes. In Christ our tastes, affections, interests and our personal dispositions change. We experience an aversion to things we use to think were great. Law could change what you did on the outside but need not affect what happened inside. That is where lining your life up with Jesus' is different.
2. A CHANGE of SLAVE MASTER V16-23 We use to be the slave of King Sin. When we were irritated he said "Be Angry...jump!" and we jumped. When hurt he said "Hit back!" and we hit back. That was our old state of thinking. We were a slave to our feelings and instincts. They gave us a flogging every day. In the end, like a slave we did this sought of thing automatically without even thinking.
In Christ we live under the fairest, kindest, most appreciative master we could dream of and are happy to be serving under his villa roof and identifying with his personal family. Paul says do you think that slave is going to wake up one morning and say "O how I wish I was back with that grumpy old slave-owner I use to belong to!" ?
3. A CHANGE of HUSBAND 7V 1-6 There is a grumpy old hard bitten husband who never thanks his wife, gambles his money, forgets her birthday, eats like a slob and demands the world from her. One day he dies. She says she will never marry again. But one day she meets the kindest, most patient, thoughtful caring man imaginable. The impossible happens. They fall in love and are married. Paul says Do you think this woman is going to wake up one morning and think "O I wish I was back with that lovely old slob of a husband I use to have!" ?
Not likely. Paul says the new husband is Christ. The old, domination by our native human passions & instincts 7V5 that just dragged us down and made life a misery.
We share the new husband's identity & surname now and want to keep it that way thank you.

So that is the power of IDENTIFICATION with Christ. We may fail at times but we are not running a performance show. We know where our hearts are. We have put on a new guernsey and have changed football teams and there's no going back to playing on the losing team. Law could never get spiritual energy happening in us like this.