Willing Salvation of Those Who Will Not

"I would pay any price to be able to say truthfully 'All will be saved.' But my reason retorts 'Without their will, or with it?' If I say 'Without their will' I at once perceive a contradiction; how can the supreme voluntary act of self-surrender be involuntary? If I say 'With their will,' my reason replies 'How if they will not give in?"

C.S. Lewis, The Problem of Pain p. 106