The Holy Spirit is the Spirit of Christ!
The Holy Spirit dwells in our heart!
But ye are not in the flesh, but in the Spirit, if so be that the Spirit of God dwell in you. Now if any man have not the Spirit of Christ, he is none of his. Romans 8:9
And because you are sons, God has sent forth the Spirit of His Son into your hearts, crying out, “Abba, Father!” Galatians 4:6