Romans 8:9 You, however, are not in the flesh but in the Spirit, if in fact the Spirit of God dwells in you. Anyone who does not have the Spirit of Christ does not belong to him. But if Christ is in you, although the body is dead because of sin, the Spirit is life because of righteousness. If the Spirit of him who raised Jesus from the dead dwells in you, he who raised Christ Jesus from the dead will also give life to your mortal bodies through his Spirit who dwells in you.
Galatians 4:6 And because you are sons, God has sent the Spirit of his Son into our hearts, crying, “Abba! Father!”
Ephesians 1:13 In him you also, when you heard the word of truth, the gospel of your salvation, and believed in him, were sealed with the promised Holy Spirit,
Ephesians 1:17-18 that the God of our Lord Jesus Christ, the Father of glory, may give you the Spirit of wisdom and of revelation in the knowledge of him, having the eyes of your hearts enlightened, that you may know what is the hope to which he has called you, what are the riches of his glorious inheritance in the saints,
2 Timothy 1:14 By the Holy Spirit who dwells within us, guard the good deposit entrusted to you.
1 John 4:4 for he who is in you is greater than he who is in the world.
Jude 1:19-21 It is these who cause divisions, worldly people, devoid of the Spirit.
This means every believer has the Holy Spirit. It is a misnomer to divide Christians among the “Spirit-filled” and the “non-Spirit-filled.” If a person is not filled with the Holy Spirit, they are not a Christian at all. However, many do miss out on living the Christian life in the constant fullness of the Spirit because they are not constantly being filled with the Holy Spirit as Paul commanded in Ephesians 5:18. They have no experience of what Jesus spoke about when He described rivers of living water flowing from the believer. How does one know that they have the Spirit? Ask these questions: Has the Spirit led you to Jesus? Has the Spirit put in you the desire to honor Jesus? Is the Spirit leading you to be more like Jesus? Is the Spirit at work in your heart?
Not only are we in Christ (Romans 8:1), but He also is in you, and because God cannot abide a sinful home, the body (old man) had to die when Jesus came in. (Guzik)
I think the problem most Christians have is that they tasted the indwelling Holy Spirit at conversion but somewhere in their life they quit listening to the Holy Spirit and reverted back to listening to what the world, worldly, and flesh has to say. They are no longer influenced and led by the Holy Spirit. The voice in their heart is that of the flesh and does what seems right in their eyes or in the eyes of the worldly. This person has no victory over sin anymore. They no longer listen for the Holy Spirit’s leading. They find comfort and peace in not being convicted of sin and are not encouraged to honor and glorify Jesus Christ. They have found it more pleasing to live in a neutral stasis thinking that living here somehow makes their lives easier to live out. There is nothing further from the truth. This is a lie from Satan and he is robbing them of power, strength, refuge, peace, hope, love, and courage, to live God-honoring, surrendered, and obedient lives. In this neutral stasis, they seek what it can not deliver or provide. How can they think they are Spirit-Filled? How can they think there is a neutral stasis? There is no neutral stasis. There is either Spirit-Filled or worldly filled. If you are not hearing the Holy Spirit speaking to your heart then it would be good to examine your heart and what is in it.