There’s a difference between being filled with the Holy Spirit versus having the Spirit live within you. Once you accept Christ as your personal Savior, you are sealed with the Spirit as a child of God. Romans 8 says:
14 For those who are led by the Spirit of God are the children of God. 15 The Spirit you received does not make you slaves, so that you live in fear again; rather, the Spirit you received brought about your adoption to sonship. And by him we cry, “Abba,Father.” 16 The Spirit himself testifies with our spirit that we are God’s children. 17 Now if we are children, then we are heirs—heirs of God and co-heirs with Christ, if indeed we share in his sufferings in order that we may also share in his glory.
ALL believers have the Spirit living in them, and there is nothing more to do to keep Him within you. You received a seal that cannot be taken away.
Ephesians 1:13 And you also were included in Christ when you heard the message of truth, the gospel of your salvation. When you believed, you were marked in him with a seal, the promised Holy Spirit, 14 who is a deposit guaranteeing our inheritance until the redemption of those who are God’s possession—to the praise of his glory.
Being filled with the Spirit requires ongoing obedience to God, who fills us with power to serve and witness to others. But it requires a conscious decision to walk with the Spirit, denying the selfishness of our flesh. This requires trusting and depending on Him, praying for strength and divine resources. Galatians 5 states:
16 So I say, walk by the Spirit, and you will not gratify the desires of the flesh. 17 For the flesh desires what is contrary to the Spirit, and the Spirit what is contrary to the flesh. They are in conflict with each other, so that you are not to do whatever you want. 18 But if you are led by the Spirit, you are not under the law.
I imagine it this way- believers have the Spirit living with them, yet we can push Him into a closet when we do not yield and submit to God. But when we invite Him to fill us with His Spirit, He fills our thoughts, feelings, and desires. He wants to fill us… we must regularly make room for Him by clearing the sin and fleshly desires from within.