For anybody who read Love Wins and was surprised by the quote from Martin Luther in it, here is the quote in context. Something Rob Bell obviously doesn’t see as important.
“If God were to save anyone without faith, he would be acting contrary to his own words and would give himself the lie; yes, he would deny himself. And that is impossible for, as St. Paul declares, God cannot deny himself (2 Tim. 2:13). It is as impossible for God to save without faith as it is impossible for divine truth to lie. That is clear, obvious, and easily understood, no matter how reluctant the old wineskin is to hold this wine–yes, is unable to hold and contain it.
It would be quite a different question whether God can impart faith to some in the hour of death or after death so that these people could be saved through faith. Who would doubt God’s ability to do that? No one, however, can prove that he does do this. For all that we read is that he has already raised people from the dead and thus granted them faith. But whether he gives faith or not, it is impossible for anyone to be saved without faith. Otherwise every sermon, the gospel, and faith would be vain, false, and deceptive, since the entire gospel makes faith necessary.” (pgs. 53-54)
Works, 43, ed. Translated by G. Wienke and H. T. Lehmann (Fortress Press, Philadelphia, PA, 1968), 53-54; WA 10.ii, 324.25-325.11)