What is the restitution of all things that Peter refers to?
The restitution of all things is the future restoration of the earth to its Edenic condition before sin entered. It occurs during the Tribulation, the seven years pictured by Revelation's seals, when the curse is reversed and the world again becomes a beautiful Garden of Eden.
Les explains that Peter says heaven must receive Jesus the Christ until the times of restitution of all things, meaning He will not stay in heaven forever. That restitution is the Tribulation, the seven years shown in Revelation chapter 5, where the seals are peeled off. Les teaches this is the road map of paying off the mortgage Satan has held since Adam fell. The earth has been under the curse almost 6,000 years, but it will be restored to its Edenic condition before sin entered, becoming once again a beautiful Garden of Eden. Peter expected the Lord's immediate return to Israel if they repented, yet he also recognized they must go through the seven years of restitution of all things.
Whom the heaven must receive until the times of restitution of all things, which God hath spoken by the mouth of all his holy prophets since the world began.