Why does the Bema judgment of believers happen in eternity instead of during the seven-year tribulation?
Because at the rapture believers receive new bodies and step out of time into eternity. The seven-year tribulation on earth is too short for the Lord to deal personally with every believer from the church age. In eternity time is irrelevant, allowing each believer specific, personal time before the Lord for reward.
Les explains that the church is raptured, meets Christ in the air, and goes back with Him into heaven while the seven years of tribulation rage on earth. As soon as believers are raptured and receive their new bodies, they step out of time and into eternity. Even though seven distinct years unfold on earth, that period multiplies into all the time in the world because believers are out of time. Les stresses it would be impossible for the Lord to deal with every individual believer from the beginning of the church age until the end in just seven years. In eternity, time is irrelevant, so all believers can have that specific, personal, quality time before the Lord for their reward.