Claim. Christ at the Second Advent cannot come merely as a spirit or as the indwelling Holy Spirit — he must come as an earthly man born in the flesh — because the providence requires him to (a) rule both the incorporeal and corporeal worlds as the perfected Lord, (b) build the Kingdom of Heaven on earth as True Parent and king, and (c) uproot original sin transmitted through physical lineage, none of which a spirit-only return can accomplish.
Elaboration. Per 2.2. Christ Will Return as a Child on the Earth, three reasons in the Principle.
Reason 1 — two-worlds dominion. God created both incorporeal and corporeal worlds and created human beings with spirit and flesh, intending them to rule both. Adam’s Fall lost this. Jesus, the perfected Adam, came as Lord of both worlds — but when his body was delivered to the cross, physical salvation was unaccomplished, and to this day no one has attained both spiritual and physical perfection. Christ cannot return only in spirit — he must come as a human being, grow to perfection in both spirit and flesh, and engraft humanity spiritually and physically.
Reason 2 — kingship on earth. Jesus was originally to restore the Kingdom of Heaven on earth as True Parent and king. Disbelief drove him to the cross with a return-promise. At the Second Advent, Christ “is again responsible to build the Kingdom of Heaven on earth and there become the True Parent and king of all humanity” — which can only be done by being born on earth.
Reason 3 — physical sin-redemption. Redemption of sins is possible only through earthly life. The cross provided spiritual salvation but did not resolve original sin transmitted through physical bodies. Complete salvation including physical-line salvation requires Christ to come again in a physical body.
Against alternative doctrines: the indwelling-Holy-Spirit SA (already happened at Pentecost); the spirit-only SA (the resurrected Jesus has appeared in spirit ever since the third day — if that were the SA, no historical advent to anticipate). When Jesus appeared to John in vision saying “Surely I am coming soon” (John replied “Come, Lord Jesus”), both distinguished spiritual appearances from the SA.
God will not violate His own Principle by housing a fleshly Christ in outer space to descend on matter-composed clouds.
See also. dp-jesus-completed-only-spiritual-rebirth-second-advent-needed-for-physical · dp-second-advent-required-to-complete-physical-salvation · dp-jesus-as-last-adam-and-tree-of-life-second-coming