Why teach gospel in spirit prison? Everyone was taught the gospel in pre-earth life so they already know it and memory will return after death.
Although, our spirits were taught the gospel as spirits with our Heavenly Father, the Lord placed a veil over our eyes that we may live by faith. Modern revelation provides us with some additional insights pertaining to our state of mind after death, and probably why it is essential the gospel is preached to them in spirit prison.
In 1 Peter 4:6,
“For for this cause was the gospel preached also to them that are dead, that they might be judged according to men in the flesh, but live according to God in the spirit.”
In this verse we recognize one reason why the gospel is preached in prison, so that they might be judge according to men in the flesh. In light of this verse let us read D&C 138:30,
“But behold, from among the righteous, he organized his forces and appointed messengers, clothed with power and authority, and commissioned them to go forth and carry the light of the gospel to them that were in darkness, even to fall the spirits of men; and thus was the gospel preached to the dead.”
This verse explains to us that the wicked are still in a state of “darkness”, implying they are without the glory of God, light and truth. This may also emphasize that the veil isn’t completely withdrawn from our minds while in prison, immediately after death.
Verse 34, provides an additional witness to 1 Peter 4:6 by specifying, “And all other principles of the gospel that were necessary for them to know in order to qualify themselves that they might be judged according to men in the flesh, but live according to God in the spirit.”
This second witness emphasizes that through this teaching in the spirit world these sons and daughters of God will be able to be judged according to men in the flesh, while living according to God in the spirit.