Why can't man be saved by his works?
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But we are all as an unclean thing, and all our righteousnesses are as filthy rags; and we all do fade as a leaf; and our iniquities, like the wind, have taken us away.
-Isaiah 64:6
For all have sinned, and come short of the glory of God;
-Romans 3:23
For by grace are ye saved through faith; and that not of yourselves: it is the gift of God: Not of works, lest any man should boast.
-Ephesians 2:8-9
And if by grace, then is it no more of works: otherwise grace is no more grace. But if it be of works, then is it no more grace: otherwise work is no more work.
-Romans 11:6