There are many things God has only given us a tiny glimmer of light on. John touches on one of those things here. "But I tell you the truth, it is to your advantage that I go away.; but If I do not go away, the Helper shall not come to you; but if I go I will send him to you."
Why couldn't the Holy Spirit and Jesus dwell on earth at the same time? What Jesus tells Mary Magdalen later is a clue. "stop clinging to me. I have not yet assented to my Father." (John 20:17). The writer of Hebrews joins in the discussion when he said, "How much more shall the blood of Jesus who through the Eternal Spirit offered himself without spot or blemish cleanse your conscience from dead works to serve the living God?" (John 9:14).
It was not that the Holy Spirit and Jesus could not dwell on earth at the same time. It was that Jesus had to appear before his Father as the completed final sacrifice that removed our guilt. The price for sin had to be paid first, before the Holy Spirit could dwell in us.
