Spirit. We said that God could not have made another way to be closer to us than what he does in the indwelling of the Holy Spirit. He does not come to stand above or below us. Nor does he stand before nor behind us nor beside us. he dwells in us.
As we talk about the Holy Spirit, we have to clarify what we mean by "spirit". Ordinarily, people associate "spirit" with ghosts. And we can partly agree with this for in former times, we used to refer to the 3rd Person of the Trinity as "Holy Ghost." But on account of the fact that English is a living language, the nuance of "ghost" has changed for the frightening. And so we now say "Holy Spirit".
But what do we mean by "spirit"? A spirit is a disembodied being that knows and wills. Angels and demons are spirits. The Holy Spirit is obviously a spirit. The difference between them is that angels and demons are created spirits (they are creatures) while the Holy Spirit is uncreated (He is God). The difference between angels and demons is that the angelic mind is oriented towards the Truth while the demonic mind is oriented towards a Lie. The angelic will is inclined towards the Good while the demonic will is inclined towards evil. Of course, the Holy Spirit's mind is the Truth (He is the Spirit of Truth) and His will is the Good (He is Holy).
The Holy Spirit dwells in our souls. We received him on the day of our Baptism. He dwells in our souls to transform our minds and orient them to the Truth (who is God). He dwells in our souls to transform our will and orient it to the Good (who is God).
On the other hand, in a demonic possession, the demon takes over (dwells) in the human body and not in the soul. His objective is very simple...he wants to kill and destroy. The father of the possessed boy said to Jesus: "It has often thrown him into fire and water to kill him." (Mk. 9 - Monday 7th Wk in Ord Time). But of course, while the devil can make the body of the possessed his plaything, he cannot enter the soul where the Holy Spirit dwells unless...the person opens the door of the soul and lets the devil enter. The devil is like a roaring lion in search for someone to devour. But he stays outside the heart until the door is opened from within and he is invited to enter. This happens in the person's willful cooperation with the devil in mortal sin. And when the door of the soul is opened to let the devil in, the person closes his heart to the Holy Spirit and rejects Him. Jesus himself said, "No one can serve two masters. He will love one and despise the other..." In mortal sin, the person loses the indwelling of the Holy Spirit whom he rejects and drives away. Losing the Holy Spirit who is the Giver of Life, the soul dies. Thus, the plan of the devil is accomplished because he came to kill and destroy. This is the reason why mortal sin is called "mortal" - it kills the soul.
The only way to revive the dead soul is by the sacrament of Confession. In the Sacrament of Confession, the Holy Spirit returns to his dwelling in response to the contrition of the penitent. the Holy Spirit brings about the forgiveness of sins and also he infuses the Divine Life into the soul. Thus, He restores what sin has taken away and once again He transform the person's mind and heart unto the mind and heart of Christ.
The indwelling of the Holy Spirit is God's most precious gift to us. Let us take care of this gift. Let us preserve the Divine Life in us through regular confession and frequent communion.