In 1 Peter 3:18, the Jehovah's Witnesses use this verse to say that Jesus was resurrected as a Spirit, is?

The Bible says that Jesus was the "firstborn of all creation" at Col 1:15, 16. That has to mean that he was created first before anyone or anything else. Why is it then hard to believe that he returned to heaven as a spirit creature after he sacrificed his perfect human life??