There are two key phrases in the next two verses. One is that we cannot inherit the celestial kingdom unless we endure to the end, the second is that if we become careless and fail to endure to the end we are assigned to one of the lower kingdoms forever. Once we have been hewn down so to speak with a resurrected body of a lower order we never can return to the celestial order of things. This is why we must endure to the end.