"Preparing a Place (Mansions) for You"

Were not the Old Testament saints not in heaven, since Jesus said He was "preparing a place for you?" [John 14, John 2:16, 1 Peter 2:5, 1 Corinthians 3:16, 2 Corinthians 6:16, 1 Peter 3:15, Ephesians 2:20-22, John 14:23, John 14:2].