The apostle Paul gave the instruction that Christians are to be filled with the Spirit in Ephesians 5:18. In Ephesians 3:16–19, Paul also noted that being filled with the Spirit is the same as having “His Spirit in the inner man,” Christ dwelling in the heart, and being “filled with all the fullness of God.” Christians are commanded to be filled with the Spirit. Romans 8 is apparent that this indwelling of the Spirit and Christ is by setting the mind on the Spirit rather than on the flesh. However, how does someone set the mind on the Spirit?
Christians set their minds on the Spirit by setting their minds on the truth that Christ’s Spirit has revealed (Rom 8:5–6). The work and mission of the Holy Spirit is to reveal all truth to Christ’s Apostles (John 16:12–13). Jesus declared that He gave His words being truth to His Apostles (John 17:8, 14, 17; 1 Cor 2:13). Jesus revealed that He had more to reveal to and through His Apostles (John 16:12–13; 17:20–21).
The apostle Paul expressed that the indwelling of Christ is by the Spirit in the inner man and reveals that the Spirit’s revelation is through Christ’s Apostles (Eph 3:3–5). Jesus revealed in John 15:4 that He, Jesus, dwells in them who dwell in Him, and Jesus declared in John 15:7 that He abides in those who have His words abiding in them. Christ abides in His followers by His words. The apostle John expressed, “Now he who keeps His commandments abides in Him, and He in him. And by this we know that He abides in us, by the Spirit whom He has given us” (1 John 3:24; cf. 1 John 4:13).
The apostle Paul also described the Holy Spirit’s mission as transforming believers back into the image of God — Christ. Paul also revealed in 2 Corinthians 3:18, “But we all, with unveiled face, beholding as in a mirror the glory of the Lord, are being transformed into the same image from glory to glory, just as by the Spirit of the Lord” (2 Cor 3:18). How does the Holy Spirit transform the followers of Christ? Paul instructed, “And do not be conformed to this world, but be transformed by the renewing of your mind” (Rom 12:2). The Spirit transforms believers through the Word, and the Spirit of Christ revealed that Word to all Christians through the Apostles and prophets of Christ. These words are spirit and life (John 6:63). Inspired Apostles and prophets wrote these words forming the Scriptures (Eph 3:3–5 2 Pet 1:16–21; 1 John 1:1–4). Thereby, the person of God can be complete unto every good work (2 Tim 3:16–17).
Christians fill themselves with the Spirit by continuing to fill themselves with the words of Christ. The indwelling of the Spirit is by the Christian setting the mind upon the Spirit (Rom 8:5–15).