He Meant What He Said -- C S Lewis

God tells us, "Be ye perfect, as I am perfect." 

From C S Lewis -- 

"The command, 'Be ye perfect" is not idealist wishing. Nor is it a command to do the impossible.

He is going to make us into creatures that can obey that command.

If we let Him -- for we can prevent Him if we choose -- He will make the feeblest and filthiest of us into a god or goddess, a dazzling, radiant immortal creature, pulsating all through with such energy and joy and wisdom and love as we cannot now imagine,  a bright stainless mirror which reflects back to God perfectly (though, of course, on a smaller scale) His own boundless power and delight and goodness. 

The process will be long and sometimes very painful, but that is what we are in for, nothing less. He meant what He said."