There are a couple of problems with this (thus some of the debates you might see on this thread, etc.) But, in my view, one of simplest objections to the 'law is a curse' argument, is just that through book after book of the Bible, no one seems to suggest it is impossible to keep, although many of the Prophets point out that there is a lot more to keeping the law than outward observances.
Some would argue that the Old Testament is abrogated by the New, but even in the New Testament we read of: 'a certain priest named Zacharias ... and his wife ... and they were both righteous before God, walking in all the commandments and ordinances of the Lord, blameless.' (Luke 1,5-6)
A standard theological response to these questions is given by John Calvin who says:
When [God] calls it a “perpetual” or eternal “covenant,” the Jews rest on it as a ground of their obstinacy, and wantonly rave against Christ as a covenant-breaker, because He abrogated the Sabbath.... Whatever was spoken of under the Law as eternal, I maintain to have had reference to the new state of things which came to pass at the coming of Christ; and thus the eternity of the Law must not be extended beyond the fulness of time, when the truth of its shadows was manifested, and God’s covenant assumed a different form. If the Jews cry out that what is perpetual, and what is temporary, are contraries to each other, we must deny it in various respects, since assuredly what was peculiar to the Law could not continue to exist beyond the day of Jesus Christ.
Your confusing the "Law of Moses" with the "Law of God."
The spiritual Law had been in effect from creation....the Law of Moses was the Law added later.
It was added because of transgressions (sin). The definition of sin? [1 John 3:4] The transgression of the Law. What Law???? God's spiritual Law that preceded "The Law of Moses!"
The civil and ceremonial "Law of Moses" is what has been done away with and is of what the Apostle speaks. Deuteronomy, chapters 27 & 28 are good examples of the Mosaic Law. Exodus 20:1-17 is a good example of the Law of God.
When [God] calls it a “perpetual” or eternal “covenant,” the Jews rest on it as a ground of their obstinacy, and wantonly rave against Christ as a covenant-breaker, because He abrogated the Sabbath.... From Dictionary.com:
ab·ro·gate (br-gt) Pronunciation Key tr.v. ab·ro·gat·ed, ab·ro·gat·ing, ab·ro·gates To abolish, do away with, or annul, especially by authority.
Jesus did not abrogate the Sabbath:
Isa 8:20 To the law and to the testimony: if they speak not according to this word, it is because there is no light in them.
Deu 13:1 If there arise among you a prophet, or a dreamer of dreams, and giveth thee a sign or a wonder, Deu 13:2 And the sign or the wonder come to pass, whereof he spoke unto thee, saying, Let us go after other gods, which thou hast not known, and let us serve them; Deu 13:3 Thou shalt not hearken unto the words of that prophet, or that dreamer of dreams: for the LORD your God proveth you, to know whether ye love the LORD your God with all your heart and with all your soul. Deu 13:4 Ye shall walk after the LORD your God, and fear him, and keep his commandments, and obey his voice, and ye shall serve him, and cleave unto him. Deu 13:5 And that prophet, or that dreamer of dreams, shall be put to death; because he hath spoken to turn you away from the LORD your God, which brought you out of the land of Egypt, and redeemed you out of the house of bondage, to thrust thee out of the way which the LORD thy God commanded thee to walk in. So shalt thou put the evil away from the midst of thee.
Note 1: the standard for judging prophets.
Joh 8:12 Then spake Jesus again unto them, saying, I am the light of the world: he that followeth me shall not walk in darkness, but shall have the light of life.
Note 2: Jesus IS the light that Isaiah references!
Mat 12:1 At that time Jesus went on the sabbath day through the corn; and his disciples were hungry, and began to pluck the ears of corn, and to eat. Mat 12:2 But when the Pharisees saw it, they said unto him, Behold, thy disciples do that which is not lawful to do upon the sabbath day. Mat 12:3 But he said unto them, Have ye not read what David did, when he was hungry, and they that were with him; Mat 12:4 How he entered into the house of God, and did eat the shewbread, which was not lawful for him to eat, neither for them which were with him, but only for the priests Mat 12:5 Or have ye not read in the law, how that on the sabbath days the priests in the temple profane the sabbath, and are blameless Mat 12:6 But I say unto you, That in this place is one greater than the temple. Mat 12:7 But if ye had known what this meaneth, I will have mercy, and not sacrifice, ye would not have condemned the guiltless. Mat 12:8 For the Son of man is Lord even of the sabbath day. Mat 12:9 And when he was departed thence, he went into their synagogue: Mat 12:10 And, behold, there was a man which had his hand withered. And they asked him, saying, Is it lawful to heal on the sabbath days? that they might accuse him. Mat 12:11 And he said unto them, What man shall there be among you, that shall have one sheep, and if it fall into a pit on the sabbath day, will he not lay hold on it, and lift it out? Mat 12:12 How much then is a man better than a sheep? Wherefore it is lawful to do well on the sabbath days. Mat 12:13 Then saith he to the man, Stretch forth thine hand. And he stretched it forth; and it was restored whole, like as the other.
Note 3: The Pharisees were testing Jesus with the Deuteronomy and Isaiah standard. They failed.
Note 4: Jesus could not say there was no more Sabbath or it has changed because if he had, he would have been contradicting the Law, he would have been stoned, and that would have been that