I will ask again. If it were possible for man to keep them. Then why did Jesus die on the Cross?
Because the law did not forgive people of sins, it was a tutor to show us our sinful ways to lead us to the only sacrifice that can truly forgive our sins. And that is through our Lord Jesus Christ.
Lord Jesus coming to die for our sins had nothing to do with being able to keep or not keep the law, plus you have to remember that the Jews also had 613 laws to go by in the mosaic covenant. All those 613 laws, written ordinances do not apply to new covenant believers. This is why Paul got on Peter, because he was trying to push the old traditional laws on new covenant converts.
I do not find having God as my only God hard, nor do I find it hard to not make idols, use His name in vain, honor my parents, not murder, not steal, not bear false witness. None of them do I find hard.
The not commit adultery is still a struggle when you go by the Lords standard, but I am being perfected by Him and if I start having those bad thoughts. I stop them before they rise and take control and then become action.
The not covet is another thing that is being perfected in me by Him. As He is teaching me how to completely satisfied with what I have and not want more. He has humbled me.
Keeping the Sabbath holy is not hard, but this one I singled out because it determines how one looks at the Sabbath still.
Some debate Saturday, some Sunday, and others we give every day to God. Plus the other way that some of us look at it is that Lord Jesus is our Sabbath rest now. In Him we have our rest.
By giving each day to Him, and showing that in my walk to follow His guidance to perfect me in the faith I feel as though I am obeying the greatest command to love Him with all my heart, soul, mind. I am letting Him guide me to better my life.
Then not holding no ill will, or hatred toward others I am following the love thy neighbor.