When Jesus talked to Nicodemus of heavenly things He said that no one could make them known except "the Son of man which is in heaven." (John 3:13)
John also tells us that: "The only begotten Son ... is in the bosom of the Father." (John 1:18)
Christ was on earth when He was talking to Nicodemus, yet He was in heaven. That is, heaven is wherever Christ is. He brings heaven to earth.
So that those who "rejoice in Christ Jesus," (Philippians 3:3) have a heaven in which to live while going to heaven. The song therefore, tells Scripture truth when it says,
Amazing grace! 'tis heaven below,
To feel the blood applied.
--Mrs. Phoebe Palmer, Hymn: The Cleansing Wave.
--Present Truth, September 13, 1894--Timeline: III-3 (Discussion with Nicodemus)--John 3:13.