How are the dead in Christ raised — what happens to the body and to the soul and spirit?

At the resurrection, the dead in Christ rise first: their bodies are brought out of the grave, wherever buried, and are reunited with their soul and spirit. Meanwhile, the soul and spirit of believers, absent from the body, are present with the Lord and are brought by God from heaven into the atmosphere for that reunion.

Les explains that the body is placed in the grave. Paul says that so far as the soul and spirit is concerned, absent from the body is present with the Lord. Then, at the coming of the Lord, God will bring those departed souls and spirits of believers only—not unbelievers—from heaven down to the atmosphere. The dead in Christ shall rise first: they are brought out of the tomb, wherever buried, and reunited with their soul and spirit, which God has brought from His presence into the atmosphere. Living believers who remain will not precede them; they will be changed in the twinkling of an eye.

1 Thessalonians 4:16

For the Lord himself shall descend from heaven with a shout, with the voice of the archangel, and with the trump of God: and the dead in Christ shall rise first:

Why do the dead in Christ rise before the living are changed at the rapture?

Scripture states that the living who remain shall not precede those asleep in Christ; the dead in Christ must rise first. Their souls and spirits are brought from heaven to the atmosphere, and their resurrected bodies are brought out of the tomb and reunited with them before the living are changed.