So in order men understand "How and What the God's Grace is " there should be manifestation of God's Grace" by the Messiah.
If men realize and admit that they are spiritually dead, means there are no any capability within them that they can depend on (even positive will ) they surely said to God " Oh God , You are so odd! How can i fulfill Your these hundreds law , if the simplest one for not eating the fruit of the tree of life intentionally i shall not be able to do ?, where as proof is : You drove me out from Eden ".
Hundreds of year God gave men to verify about their "spiritually dead" began from the Torah laws until the cross , men didn't realize any yet, men persistently enthusiastically trying to fulfill the laws ( working in Sabbath day/salvation by work) so manifestation of the God's Grace was necessity for opening the men eyes by force ,even until now there are so many men sure they still have the positive will to obey God by themselves , this is so really sad.