John 3:16 is a magnificent verse. The Lord guarantees that whoever believes in Him will not perish (= be eternally condemned, John 3:17), but has everlasting life right now as a present possession. Believers will live forever in the sense that they have everlasting life and always will. Unbelievers will have conscious existence forever, but they will only live forever if they come to faith in Christ for everlasting life before they die.