Well, nobody is able to fulfill the commandments without Jesus, so the commandments shows what's necessary for salvation and humans will fail by trying this with their own Power.The missunderstood by this question is some people think it means we could earn our salvation with works, what means to change the right succession.

EXAMPLE:"Ephesians 2:8-9" makes clear nobody can "earn" his salvation, that we're saved through faith and Grace.Nevertheless "Ephesians 2:10" shows us works are important, because they're "fruits of salvation", a result which God prepares for humans who were saved!

CONCLUSION:Nobody can earn his salvation with works, but when he was saved the requirement to do good works is a result of salvation, what means humans who don't want to do good things for the Lord never were saved before (Ephesians 2:10).

CONCLUSION2:Saved people do not fail when they follow Jesus Christ, because the Law is "written in their heart" (thanks to our savior), that's the meaning in "Matthew 5:17", when he said what the Lord did for us.