Well, we are talking about a Covenant made by God here and not mere humans. The parallel is just to help to illustrate that the Testament (i.e. the New Testament) did not go into force until the Testator died. Meaning, the New Testament began with Christ's death.
You also have to keep reading, too.
For Hebrews 10:1 says,
For the Law having a shadow of the good things to come, and NOT the very image of the things, can never with those sacrifices which they they offered year by year continually make the comers thereunto perfect.
OK, since you brought up Hebrews 10, let's read it in context and see what it is discussing...
Heb 10:1 For the law having a shadow of good things to come, and not the very image of the things, can never
with those sacrifices which they offered year by year continually make the comers thereunto perfect.
What is being shadowed here is revealed in the very first verse. The subject is the animal sacrifices performed by the Aaronic Priesthood. And what about those sacrifices?
"can never...make the comers thereunto perfect."
So the subject is sacrifices. If the subject in a newspaper article was about crime in the Lower East Side of New York would you try to apply it to the Ebola outbreak in Monrovia? The subject is animal sacrifices not the Ten Commandments.
So let's read on...
Heb 10:2 For then would
they not have ceased to be offered? because that the worshippers once purged should have had no more conscience of sins.
Heb 10:3 But in those
sacrifices there is a remembrance again made of sins every year.
Heb 10:4 For it is not possible that the
blood of bulls and of goats should take away sins.
Heb 10:5 Wherefore when he cometh into the world, he saith,
Sacrifice and offering thou wouldest not, but a body hast thou prepared me:
Heb 10:6 In
burnt offerings and sacrifices for sin thou hast had no pleasure.
Heb 10:7 Then said I, Lo, I come (in the volume of the book it is written of me,) to do thy will, O God.
Heb 10:8 Above when he said,
Sacrifice and offering and burnt offerings and offering for sin thou wouldest not, neither hadst pleasure therein; which are offered by the law;
So reading up to verse 9, what is the author (I believe this to be Paul but YMMV) writing about? What is the subject matter?
Obviously animal sacrifices.
Now let's read verse 9 in context...
Verse 9 then clarifies that the Old Testament is taken away so that the second Testament (i.e. the New Testament) would be established:
"Then said he, Lo, come to do thy will, O God. He taketh away the first, that he may establish the second." (Hebrews 10:9).
The taking away of the first is in reference to the "first testament" spoken of in the previous chapter (See Hebrews 9:15, 18, 19); And the New Testament is referred to as a contrast to the "first testament" in verse 15 and is called the "New Testament." (Which would obviously be the second or second testament).
No, he is not jumping back to the previous chapter, although, if you really want to reference chapter 9, please read it...
Heb 9:7 But into the second went the high priest alone once every year, not without blood, which he offered for himself, and for the errors of the people:
Heb 9:8 The Holy Ghost this signifying, that the way into the holiest of all was not yet made manifest, while as the first tabernacle was yet standing:
Heb 9:9 Which was a figure for the time then present, in which were offered both gifts and sacrifices, that could not make him that did the service perfect, as pertaining to the conscience;
Heb 9:10 Which stood only in meats and drinks, and divers washings, and carnal ordinances, imposed on them until the time of reformation.
Heb 9:11 But Christ being come an high priest of good things to come, by a greater and more perfect tabernacle, not made with hands, that is to say, not of this building;
Heb 9:12 Neither by the blood of goats and calves, but by his own blood he entered in once into the holy place, having obtained eternal redemption for us.
Heb 9:13 For if the blood of bulls and of goats, and the ashes of an heifer sprinkling the unclean, sanctifieth to the purifying of the flesh:
Whoa, here we are again referencing the fact that animal sacrifices could not make whom? The High Priest, verse 7, perfect, nor was he the Sacrifice and High Priest that was to come. The High Priest was a type, a shadow of the coming of the true High Priest: Christ.
This passage is not speaking of the replacement of the Old Covenant. We do not reach that point until we read verses 15 on. Now, with some context in mind, let's read the remainder of chapter 9...
Heb 9:15 And for this cause he is the mediator of the new testament, that by means of death, for the redemption of the transgressions that were under the first testament, they which are called might receive the promise of eternal inheritance.
Heb 9:16 For where a testament is, there must also of necessity be the death of the testator.
Heb 9:17 For a testament is of force after men are dead: otherwise it is of no strength at all while the testator liveth.
Heb 9:18 Whereupon neither the first testament was dedicated without blood.
Heb 9:19 For when Moses had spoken every precept to all the people according to the law, he took the blood of calves and of goats, with water, and scarlet wool, and hyssop, and sprinkled both the book, and all the people,
Heb 9:20 Saying, This is the blood of the testament which God hath enjoined unto you.
Heb 9:21 Moreover he sprinkled with blood both the tabernacle, and all the vessels of the ministry.
Heb 9:22 And almost all things are by the law purged with blood; and without shedding of blood is no remission.
Heb 9:23 It was therefore necessary that the patterns of things in the heavens should be purified with these; but the heavenly things themselves with better sacrifices than these.
Heb 9:24 For Christ is not entered into the holy places made with hands, which are the figures of the true; but into heaven itself, now to appear in the presence of God for us:
Heb 9:25 Nor yet that he should offer himself often, as the high priest entereth into the holy place every year with blood of others;
Heb 9:26 For then must he often have suffered since the foundation of the world: but now once in the end of the world hath he appeared to put away sin by the sacrifice of himself.
Heb 9:27 And as it is appointed unto men once to die, but after this the judgment:
Heb 9:28 So Christ was once offered to bear the sins of many; and unto them that look for him shall he appear the second time without sin unto salvation.
And what we are reading here is that Christ became the payment for sin. Sin still is the transgression of the Law...
Rom 7:7 What shall we say then? Is the law sin? God forbid. Nay, I had not known sin, but by the law: for I had not known lust, except the law had said, Thou shalt not covet.
1Jn 3:4 Whosoever committeth sin transgresseth also the law: for sin is the transgression of the law.
And there is no sin without Law...
Rom 4:15 Because the law worketh wrath: for where no law is, there is no transgression.
Rom 5:13 (For until the law sin was in the world: but sin is not imputed when there is no law.
When you read Matthew 5:18, you have to also read the verse that is right before it. Verse 17 makes reference to the "Law and the Prophets." This is what verse 18 is referring to when it uses the word "Law." In other words, the word "Law" refers to the Law AND the Prophets (i.e. the Old Testament writings). The Law was fulfilled with Christ's death. But there are still prophecies (Which is a part of what is called the Law) in the Old Testament that Christ needs to still fulfill. Luke 16:17 says the same thing. Look at verse 16 before it. The word "Law" in verse 17 is in reference to the words "Law and the Prophets" in verse 16.
Uh, that is not what Matthew 5 says, that is what you wish it said. Don't tell us that it says one thing but really means something else, what it really says is just what it says...
Mat 5:18 For verily I say unto you, Till heaven and earth pass, one jot or one tittle shall in no wise pass from the law, till all be fulfilled.
Maybe the NKJV helps here...
Mat 5:18 For assuredly, I say to you, till heaven and earth pass away, one jot or one tittle will by no means pass from the law till all is fulfilled.
Not a jot or tittle will pass from the Law until heaven and earth pass away. Now, I am not sure what parallel universe you live in but the one I live in still has heavens and an earth.
The problem of sin and the payment for sin is not solved by doing away with the Law. That is an affront to Christ who DIED to pay the penalty for transgressing the Law. If He came to do away with the Law, and He is the Lawgiver...
Jas 4:12 There is one lawgiver, who is able to save and to destroy: who art thou that judgest another?
The simple solution would be to simply do away with the Law. He chose rather to pay the penalty for breaking the Law. If the Law is done away and you believe Rom 4:15 and 5:13, then there is no sin and you don't need a Savior, there is no sin to save you from.