“Be filled with the Spirit” is a command (Eph 5:18). How can this be a command? How do Christians allow themselves to be filled with Holy Spirit? What control do Christians have over being filled with Spirit? Evidently, Christians do have a way to obey the command to be filled with the Spirit. Being filled with the Spirit includes “His Spirit in the inner man,” Christ dwelling in the heart, and being “filled with all the fullness of God” through being grounded in love and comprehending the love of Christ (Eph 3:16–19). This is the indwelling of the Spirit and being filled with the Spirit in contrast to being filled with wine and dissipation (Eph 5:18).
Eternal life and resurrection in Christ is determined by whether the Spirit of Christ dwells within the believer. The apostle Paul revealed in Romans 8:9–11,
But you are not in the flesh but in the Spirit, if indeed the Spirit of God dwells in you. Now if anyone does not have the Spirit of Christ, he is not His. And if Christ is in you, the body is dead because of sin, but the Spirit is life because of righteousness. But if the Spirit of Him who raised Jesus from the dead dwells in you, He who raised Christ from the dead will also give life to your mortal bodies through His Spirit who dwells in you.
What was Paul referring to as the indwelling of the Spirit? How does the Holy Spirit dwell within Christ’s followers? How the Spirit dwells within Christians is revealed in Romans 8:5–6, “For those who live according to the flesh set their minds on the things of the flesh, but those who live according to the Spirit, the things of the Spirit. For to be carnally minded is death, but to be spiritually minded is life and peace.”
This is the context of the indwelling of Christ and His Spirit in Romans 8:9–11. The Spirit must dwell in the mind, and Christians have the ability to set their minds on the Spirit. This is in contrast to the carnal mind being enmity against God and not subject to God’s law (Rom 8:7–8). When the believer is in the Spirit, then the Spirit dwells in that person and so does Christ dwell in that person. By the Spirit’s indwelling, then believers are Christ’s and they have life. Here is the indwelling of Christ and His Spirit and this is how one is filled with the Spirit: “those who live according to the Spirit set their minds on the things of the Spirit” (Rom 8:5).
The Breath of God 
Here is one insight on how to be filled with the Spirit.
Psalm 46:10, Be still, and know that I am God:
There are many words written and preached about the indwelling of the Holy Spirit. You have written a simple and meaningful explanation based on scripture. Thank you for your simplicity.