If I put “Christ in me” first then I fall for a Catholic doctrine of infusion. God infuses His grace into me so that I begin to live the righteous life. Eventually I might be declared righteous. If a person gives priority to “Christ in me” they may have Personalised the grace which God gives (which is an improvement on the Catholic doctrine) but we’re still travelling along the same route.
The gospel is “I in Christ” – that is, through a gracious marriage union with Christ I immediately have His name. Therefore righteousness is a status instantly imputed to me as a gift in Jesus.
The phrase “in Christ” is used 150 times by Paul. I haven’t counted them, but I’m guessing the teaching of “Jesus in me” occurs significantly less frequently!
The rest of my Christian life involves a communion with Jesus in which I gradually exhibit more and more of His nature. But that is not my hope. My hope is not me living Christ’s life (even if it’s by His power within me). My hope is Christ living my life (with me hidden in Him).
The sacraments teach this fundamental truth. I am baptised into Christ. This is the beginning and foundation of my Christian life – I in Christ. But regularly I am fed by Christ and take Him into myself – Christ in me.
To put it in Passover terms, I am saved once and for all by the Lamb’s blood applied externally – I’m hidden in the Lamb. But I am nourished for the journey out of Egypt by the Lamb’s flesh – the Lamb in me.
And incidentally this is the basis of the Christian sexual ethic too. The once-for-all one-flesh union first, the regular one-flesh communion afterwards – the two utterly united and the former given absolute priority.
Mix them up and you get into all sorts of trouble, in all areas of life!