People who do not acknowledge God are cut off from the church because the whole point of the church is God, and because the things related to God that are called theological teachings give the church its structure. Therefore to deny the existence of God is to deny everything having to do with the church. The denial itself is what cuts them off; that is, they cut themselves off. God does not cut them off.
They are damned as well because those who are cut off from the church are also cut off from heaven. The church on earth and the angelic heaven act as a unit, just like the inner and outer self, and like the spiritual part and the physical part in each of us. God created us in such a way that our inner self is in the spiritual world and our outer self is in the physical world. Therefore to make us permanent and everlasting beings, God made us citizens of both worlds so that the spiritual part of us, which belongs in heaven, could be planted in the physical part belonging to this world the way a seed is planted in the ground.
People who cut themselves off from the church and from heaven by denying the existence of God close their inner selves on the side of the will and shut themselves off from its positive love. (The will in us is a vessel for love and becomes its dwelling place.) Their inner selves on the side of the intellect, however, they are unable to close, because if they could and did they would no longer be human; but [evil] love in their will does befuddle their higher intellect with false ideas. As a result, their intellect becomes virtually closed to truths related to faith and good qualities related to goodwill and becomes more and more closed to the Lord and the spiritual teachings of the church. As a result, those denying the existence of God lose their partnership with angels in heaven. Once that is gone, they establish a partnership with satans in hell and think what the satans are thinking. All satans deny the existence of God and have absurd thoughts about God and about the church’s spiritual teachings; and so do people on earth who are in partnership with them.
from True Christianity, Volume 1, Section