Heaven, the abode of God, the place where God manifests him/it self to the blessed, a condition of grace with God.
Heaven is one of the many synonyms for God-self-realization, i.e., spiritual enlightenment, also called Samadhi, Tao Satori, Nirvana, the kingdom of God, etc. etc.
Heaven is not a place; it is a condition and state of existence and be-ing.
The astral plane or astral world is not Heaven, early Christian mystics refereed to the astral plane as purgatory, the astral plane is a place where the soul understands the lessons it needs to experience and then reincarnates back into the earth plane to experience life, undo Karma, and try again to attain (actually return to) spiritual enlightenment and therefore never having to reincarnate again.
Nor will they say, See here! Or see there! For indeed, the kingdom of God is within you."
-Jesus, Luke 17:21
Most assuredly, I say to you, unless one is born again, he cannot see the kingdom of God.
-Jesus, John 3:3
Without a doubt, if you do not become reestablished back to your true and natural state of being as the new-man, the heavenly man (or woman) you cannot understand the condition of living as and in the spiritual condition.
The FIRST BIRTH is the being born into the world.
The SECOND BIRTH, born again, is when a person returns to their original spirit-self.
The FIRST DEATH, is the death of the psychological personality after it dissolves through non use because the soul, the real eternal you is no longer entangled by it.
The SECOND DEATH is that of the physical body, the divine animal, vessel or temple of the Holy Spirit.
To get to heaven is the goal of life, but one cannot go to heaven after one dies, one must attain (return to) the condition of heaven BEFORE the physical body dies or one reincarnates by the grace of God to try again and again so that NO SOUL SHALL STAY APART FOREVER (the only will of God).
There are many heavens or centers of spiritual consciousness. The Chakra's can rightfully be called heavens and the seventh heaven or the Sabbath is the highest in the body. There are some that are outside of the body. Some traditions only discover seven others discover nine centers.
The position of the many religions is that mankind is UNFIT to enter heaven. They FAIL TO UNDERSTAND that the outer man or first man the psychological-person was NOT MENT FOR HEAVEN IN THE FIRST PLACE, it is the INNER MAN, the REAL YOU, the SOUL, that must RETURN to the heavenly state.