Being a human is a gift.
It's such a cool gift that some of the angels coveted it.
Being "redeemed" has nothing to do with whether a person is changed into a spirit creature or not. The "changing into a spirit creature" is illustrative of how the priests had to change their clothes to work in the temple then they'd change back for secular duties.
Angels can materialize. Spirit creatures can materialize, but they aren't supposed to have sex and procreate.
The 144,000 are to be changed into spirit creatures for a specific purpose. They lose one gift and get another, but they are not any more "special" than anyone who stays as a human.
The heavenly government comes down out of heaven which means the 144,000 and Jesus and Jehovah will all materialize bodies and hang out here on earth with humans.
"All things are possible with God."