Something I think the Lord has been teaching me recently is to prize both these truths:
I am in Christ
Christ is in me
I am clothed in an alien righteousness but also filled with an outworking Power. My standing before God is entirely outside myself - in Jesus. Yet my walk in the world is enabled by an energy that is no less heavenly in origin but that springs from a new core within - the new heart. Will's sermon on the New Birth is a great help in this direction.
Here are some more thoughts from Watchman Nee's little book on Ephesians - Sit, Walk, Stand. In this section he is moving from our 'seated' reality with Christ in the heavenly realms (Eph 1-3) to our 'walk' in the world (Eph 4-5).
God has given us Christ. There is nothing now for us to receive outside of Him. The Holy Spirit has been sent to produce what is of Christ in us; not to produce anything that is apart from or outside of Him...We have been accustomed to look upon holiness as a virtue, upon humility as a grace, upon love as a gift to be sought from God. But the Christ of God is Himself everything that we shall ever need... Our life is the life of Christ, mediated in us by the indwelling Holy Spirit Himself.
No wonder that this is Paul's prayer as he transitions from the 'seated' reality to our earthly 'walk':
14 For this reason I kneel before the Father, 15 from whom his whole family in heaven and on earth derives its name. 16 I pray that out of his glorious riches he may strengthen you with power through his Spirit in your inner being, 17 so that Christ may dwell in your hearts through faith. And I pray that you, being rooted and established in love, 18 may have power, together with all the saints, to grasp how wide and long and high and deep is the love of Christ, 19 and to know this love that surpasses knowledge--that you may be filled to the measure of all the fulness of God. (Eph 3:14-19)