The Jews were told over and over again not to come to G-d in a prefunctiary manner. To only come to do the sacrifices as something that they had to do - instead of out of want and love - repulsed G-d. G-d repeatedly told them, throughout Isaiah especially, but also through David's writting, that to follow the Law as a chore means nothing to G-d.
Which could be what Jesus is getting at. Just because you follow the Law does not mean you are following G-d. Just because someone washes their hands, or makes sacrifices, or says the right words does not make them right with G-d.
But does this really mean that Jesus is saying that the commandments should be tossed out the window for what Paul introduced as Christianity? No. The Law was given by G-d - an eternal covenant between Him and His people. No where does it say that such a change as introduced into Christianity was going to happen. The covenants are everlasting. Period.
And, for the argument that's probably going to come, how can Jesus be the fulfillment of something that was already completed? The Messiah is to lead the world to follow G-d - but to say that Jesus fulfills the Law means that something was lacking to begin with. That G-d gave an imperfect system to be followed. How can that be - when the Law is a gift, engraved on our hearts so that we can know G-d and do His will fully?
The verses you quoted only show how people fail when they go on their own. Not when the follow the Law.
No one is saying the commandments should be tossed out. The only way we could ever possibly keep the commandments is through Christ's strength. "I can do all things through Christ who strengthens me." And in another place the bible says, 'Not by might nor by power, but by my Spirit,' says the LORD Almighty. (Zachariah 4:6) And even if we do not keep the commandments we have God's grace through Jesus Christ. Jesus Christ is our advocate when we fail. When you're trying to keep the commandments on your own strength, grace is not involved (something we all desparately need). Personally, I do not want God's justice for my life - I want his grace and mercy. If I get justice, I'm in trouble.
Why in the world would G-d create an everlasting covenant of salvation with his chosen people if they couldn't do it? Ever?
Or toss in the caveat that we all need Jesus in order to do so - and then not provide this missing link for a few thousands years?
The answer is that He did not do this. G-d gave the Law because we could fulfill it. We don't need Jesus to do it. Instead we do it with G-d alone.
You start by loving G-d with your whole being, as he has asked us to. Then following his commandments and doing his will comes simply - and we do it with great joy.
Christians often argue that G-d is a just G-d. Then they say that they are under his grace. Does this mean that you are not going to be exposed to G-d's justice? No, not at all. Even in your own scriptures, in Revelation, there is a judgement for both beleivers and non-believers.
Fortuantely for all of us G-d's mercy is infinte. He does not demand perfection from a creation he knows cannot achieve this. Nor will he judge on us on a failure to be perfect.
The Law is a gift - a beautiful blessing. It is not a burden, a prison or a chore. It is not something to be done with drudgery or even fear but with relish and love. And to follow the Law is completely possible with out Jesus. No one said one was to follow the Law without G-d. G-d said this was not his wish time and time again.
And if you want an example of where it is possible to follow the Law without Jesus look at the parents of John the Baptist. They were doing this before Jesus' birth.
But Abraham's faith was credited to him as righteousness, and Elizabeth said that John leaped for joy when Mary came by to visit because of Jesus of Nazareth being in her womb. EmmaG, you have totally been one who tasted grace then fell away. Jesus of Nazareth is Messiah, whether you like it or not.