"14 For this reason I bow my knees before the Father, 15 from whom every family in heaven and on earth is named, 16 that according to the riches of his glory he may grant you to be strengthened with power through his Spirit in your inner being,17 so that Christ may dwell in your hearts through faith—that you, being rooted and grounded in love, 18 may have strength to comprehend with all the saints what is the breadth and length and height and depth, 19 and to know the love of Christ that surpasses knowledge, that you may be filled with all the fullness of God.
20 Now to him who is able to do far more abundantly than all that we ask or think, according to the power at work within us, 21 to him be glory in the church and in Christ Jesus throughout all generations, forever and ever. Amen."
Ephesians 3:14-21
As to details in the prayer, the Apostle's phrase in 16, 'the inner man' does not mean 'the new man' as such, but rather the soul as distinct from the body (the phrase is used similarly in 2 Corinthians 4:16, 'though our outward man perish, yet the inward man is renewed day by day', and in Romans 7:22, 'I delight in the law of God after the inward man'). As one commentator puts it the phrase refers to 'all faculties, intellectual, moral, emotional, that make up the spiritual nature - reason, conscience, will, mind, affection'. Another commentator says it is 'our central and highest life, the noblest portion of our being, the seat of our intellectual and spiritual life with its impulses, feelings arid struggles, the hidden man of the heart, the rational moral self, our whole conscious personal being, in short, our true personality'. This 'inner man' in the unregenerate is darkened, being in subjection to the power of sin in the flesh; but when quickened by the Spirit of God, it becomes 'the new man', and the sphere of the divine operations. It is here that Paul prays that God will work His gracious purposes.
It is in the heart and core of the personality, then, that Paul prays the Ephesians will be strengthened, and it is significant that the word 'in' in 16b has the force of 'into' in the original Greek. The implication is that the Holy Spirit penetrates into the deep recesses of the heart, and this should do much to explain the painfulness that a true ministry of the word involves for those who take it seriously, for it is through the Word that the Spirit effects this strengthening. If our real need lies in the deeper levels of our personality, it is precisely there, and not on the surface, that the renewing and strengthening work must take place and to get there, much probing needs to be done. To be made strong where once we were weak requires a work of no mean depth and quality; but those who respond resolutely to the buffetings of the word will, over the months and years, assuredly be changed.