Saint Nikolai Vlimrovic gives us an answer to the question with the following text.
You asked somebody, “where is God?” And you got an answer that God is inside you. And you marvel at this answer. How can that be?
Kind of like light in a room, or like fire in a; stove. When you are able to feel God within you, you will feel and know that He is inside you, but you will not be able to explain it to someone else. But you will look for images in nature and then you will speak to the other person as I speak to you: God is within me like light in a room, or a like fire in a stove, or like air in the lungs, or like life in every creature, or like force and love and thought inside of man. Of course, these are just images and likenesses, and they cannot express what a man feels when God dwells within him in His fullness. God’s apostle, our spiritual father Paul, wishes for the faithful to be filled with all fullness in God (Eph. 3, 19). God works from within a man in two ways — by helping and by governing.
When helping, God works within a man of medium or weak faith, who only occasionally remembers God and only keeps His Commandments partially. God does not abandon him because he also does not completely abandon God. However, God acts through governing in a man of great faith, who has opened wide the doors of his soul to his Creator. And it is written, “He who opens the door I will enter to him” (Rev. 3, 20). Such a man does not rely on himself at all but only on the Almighty. He feels the presence and the working of the Spirit of God within himself and has great love toward his Lord. And Christ has promised to the one who loves God that God will come and dwell within him. “He who loves me will keep my word and my Father will love him. And we will come to him and will make our abode within him.” You will not be able to understand this. If you forget that God is a Spirit, who can enter everything and be everywhere, according to his power, and will. He is high above all matter, like the Sun is high above the earth but its light can enter every open thing. As the apostle says: “One God and the Father of all who is above all and through all, and in us all” (Eph. 4, 6). He writes this about the holy and the faithful.
But when someone rejects God, starts thinking ugly thoughts and speaking against God, God also leads him. It is the same as if somebody would close off the windows of a room and prevent the light from coming in and illuminating everything. For God’s prophet Samuel said to the self-willed King Saul, “You have rejected the word of the Lord and for this the Lord has rejected you… and the spirit of the Lord abandoned Saul.” But even one God abandons a soul of a stubborn man, He does not stop working on him from without, the way he works on water and stone and wood. But if a man remains stubborn and resists God until the end and refuses to repent, then God allows an evil spirit to enter in. Like it is written about Saul when the Spirit of the Lord abandoned him, “and an evil spirit disturbed him from the Lord”. Or as it is written, even worse, about Judas the betrayer, “Satan entered into him”.
Such people, who rise against God, of course, can never feel God within themselves or say, “God is inside of us.” And those who love God, and desire Him, and see Him, and entreat Him to come they feel God within themselves and they can say, “God is within us by His Holy Spirit.” Blessed are such bright souls, for they will always reign in the kingdom of Christ. As the Lord has promised to those who love Him saying, “I will take you to myself so that you may be where I am.”