Note 5 at Eph. 3:16: Paul's prayer is a sermon in itself on how to walk in the fullness of God. The first thing Paul mentions is the Lord strengthening us through the power of the Holy Spirit. Many well-meaning Christians fall quite short of what God wants them to be and what they want for themselves because they are trying to live for God instead of letting God live through them (see note 1 at Rom. 7:15, p. 789). The key to all victory in the Christian life is learning how to depend on the Holy Spirit for our strength (see note 14 at Gal. 2:20, p. 1063).

Those who are not born again can never be victorious in the Christian life because God is not indwelling them. Even Christians who have the Lord inside of them will not experience victory apart from dependence upon the Holy Spirit. All power for the believer originates from the Holy Spirit (see note 5 at Acts 1:8, p. 573).

Note 6 at Eph. 3:16: This strengthening of the believer is done, not in the spirit, which is complete and perfect in Christ (see note 3 at Mt. 26:41, p. 507; 1 Cor. 6:17), but within the heart (see note 3 at Mt. 12:34, p. 188), i.e. the soul and personality of the believer (see note 17 at 2 Cor. 4:16, p. 999). The "inner man" referred to in this verse is also called "the inward man" in 2 Corinthians 4:16. There Paul said his inward man was being renewed day by day. This is not speaking of his spirit since it is complete in Christ Jesus (Col. 2:10).

So, our born-again spirits have already been strengthened with might through the power of the Holy Spirit. But Paul is praying that this strength would manifest itself in the Ephesians' character too. This is not speaking of the initial indwelling of Christ at conversion (Rom. 8:9) but rather the indwelling of Christ within the believer's whole personality. This happens by faith as the believer invites Christ to be at home within his soul, thus resulting in the Spirit's control of both attitude and conduct.

This happened throughout the book of Acts. Believers who were already baptized with the Holy Spirit were filled and strengthened with God's might. One of the more notable examples of this was in Acts 4:31.