The spirit, is a reference to the spirit of God, often times referred to as the Holy Ghost, or in more modern times referred to as the Holy Spirit. This is a reference to the third person of the Trinity.
With the world in desolation, at the end of the tribulation, the second advent of Christ will occur, and shortly thereafter the millennial reign of Christ will begin.
At the beginning of this reign, and almost immediately there will be a universal pouring out of the Holy Spirit upon the earth.
Just as when the earth was made null and void by the destruction caused by Satan, way back before Adam, and the Holy Spirit moved over the face of the earth and began its restoration in preparation for the human race, so too, at the second advent of Christ, the Holy Spirit will pour out across the face of the earth and begin an almost instantaneous restoration, from the destruction that has been caused by the tribulation.
The spirit from on high, is a reference to heaven.
The earth will not heal itself. Man cannot heal the earth. The earth is not capable of healing itself, despite the claims of environmentalists. Man is not capable of healing the earth.
The destruction of the planet is caused by sin, and the healing of the planet is caused by the Holy Spirit.
From the wilderness or the destruction of the planet, fields will become fruitful, fields will turn into forests. And this indicates a pattern of restoration, as the Holy Spirit moves across the face of the earth, and restoration will occur immediately, and right before the eyes of those that are present, namely all survivors of the tribulation, as well as all believers who have returned with Christ at the second advent, along with all angels.
At that time, we will witness the restoration of the earth, just as the angels witnessed the reconstruction of the earth a long time ago.