Zac Poonen preaches about the end of time, emphasizing the transition from time to eternity where redeemed individuals will enter the new heaven and new earth, as depicted in Revelation 21. He highlights the removal of Satan and unbelievers from this perfect existence, where sin and fleshly desires will no longer exist. The sermon conveys a vision of a glorious universe filled with those who have joyfully chosen to follow God's will for eternity.