I'd have thought that was perfectly obvious. They're part of Scripture, and there are several statements in the New Testament, one of which I cited, indicating that they still apply. There are also statements, as you correctly cited, that can be read as indicating they don't. So which is it?
I hope this answer doesn't bore or confuse you, but the answer to this is one that is found by referencing a little bit from a lot of different places in Scripture. The answer is we are under the teachings of Jesus. The how and why is the long and complicated (finding all the little tid-bits).
The original 10 commandments (10 Laws) were given exclusively to God's chosen people (Israel). The laws of social behavior were also exclusive to Israel, administered by the priests who could only come from the house of Levi, Aaron was their first priest, he was also a brother to Moses.
The last high-priest (from the tribe of Levi AND anointed by God) was John the Baptist. His father was a priest (Levite)and his mother was a daughter of Aaron. Jesus's lineage through Joseph includes David, heir to the throne (Matthew), His lineage through Mary (Elizabeth's cousin, making her also a daughter of Aaron) goes back to Adam. That is why (as a Son of Man, being born by a flesh and blood mother) Jesus has authority, as a priest in this case, that includes not only all of Israel but also everybody else that was ever born. Any instruction He has given (by Himself before the cross or through the words that were written after the cross has the authority as coming from one who can determine how things are. What He taught was not from Himself, those instructions were given to Him by God.
Joh:8:26:
I have many things to say and to judge of you:
but he that sent me is true;
and I speak to the world those things which I have heard of him.
Joh:8:27:
They understood not that he spake to them of the Father.
Joh:8:28:
Then said Jesus unto them,
When ye have lifted up the Son of man,
then shall ye know that I am he,
and that I do nothing of myself;
but as my Father hath taught me,
I speak these things.
Joh:8:29:
And he that sent me is with me:
the Father hath not left me alone;
for I do always those things that please him.
The change in priest-hood occurred when John was cast into prison, that is when Jesus began to preach (and heal people, etc). The Gospel of John is the only Gospel that covers things that He did before John was cast into prison, other than have His disciples baptize (in the same manner as John did) Jesus was rather 'laid-back'.
When there is a change in priest-hood (in that He was priest over more than just Israel) there also is a change in Law. The 10 original commandments were not changed other than to be made into two Laws. The 1st one being exactly the same as the 1st Law of the 10. The other 9 were changed in that they were no just 1 Law, Love thy Neighbor. Not love thy neighbor who is the same 'faith'. A neighbor to a Gentile is all other Gentiles, plain and simple.
Heb:7:11: If therefore perfection were by the Levitical priesthood, (for under it the people received the law,) what further need was there that another priest should rise after the order of Melchisedec, and not be called after the order of Aaron?
Heb:7:12:
For the priesthood being changed,
there is made of necessity a change also of the law.
Heb:7:13:
For he of whom these things are spoken pertaineth to another tribe,
of which no man gave attendance at the altar.
Heb:7:14:
For it is evident that our Lord sprang out of Juda;
of which tribe Moses spake nothing concerning priesthood.
Heb:7:15:
And it is yet far more evident:
for that after the similitude of Melchisedec there ariseth another priest,
Heb:7:16:
Who is made,
not after the law of a carnal commandment,
but after the power of an endless life.
With a new priest-hood also comes a new covenant, the one in Hebrews 8 is the covenant that will be 'in effect' only after His second coming, that isn't in place today for either the Gentiles or the Jews. The covenant we are under is this one.
Joh:15:10:
If ye keep my commandments,
ye shall abide in my love;
even as I have kept my Father's commandments,
and abide in his love.
Joh:15:11:
These things have I spoken unto you,
that my joy might remain in you,
and that your joy might be full.
Joh:15:12:
This is my commandment,
That ye love one another,
as I have loved you.
Same answer, really; the rejection is of the messages and instructions from the "One True God," regardless of when they were delivered, and the old rules still apply. Reject it and die. Or maybe not...
But the old instructions don't apply, your references to Israel entering the promised land (and doing what they were instructed to do) ended when they finally got to their promised land, within those well defined borders. They weren't spreading the Gospel, their intent was to conquer a certain piece of land, which God also took away from them on more than one occasion, the last one still being in effect until Christ's return. If God would exile His people for not doing what He said just what do you think Christ is going to do to those that call Him lord yet do not do the things He has said? It won't be the fiery lake but it will be the closest thing to it that allows for an exit. How many 'Christians' do you think that will include? That will be the first group to be judged.
1Pe:4:15:
But let none of you suffer as a murderer,
or as a thief,
or as an evildoer,
or as a busybody in other men's matters.
1Pe:4:16:
Yet if any man suffer as a Christian,
let him not be ashamed;
but let him glorify God on this behalf.
1Pe:4:17:
For the time is come that judgment must begin at the house of God:
and if it first begin at us,
what shall the end be of them that obey not the gospel of God?
1Pe:4:18:
And if the righteous scarcely be saved,
where shall the ungodly and the sinner appear?
1Pe:4:19:
Wherefore let them that suffer according to the will of God commit the keeping of their souls to him in well doing,
as unto a faithful Creator.
Trouble is, the Bible's a sufficiently large and complex document that you can probably find support in it for any position you'd care to take.
Certainly people do that, God also put in measures that curtail that sort of practice. Any subject that is covered in Scripture is spoken of in more than one place, three or more is more usual than not. The neat thing about that is each separate reference adds just a tad-bit more information on that one topic but they usually also reference another 'similar topic'. For instance a few verses from the OT about prayer also hold a reference to 'how useful' prayer will be in that last few years before His return.
De:4:29:
But if from thence thou shalt seek the LORD thy God,
thou shalt find him,
if thou seek him with all thy heart and with all thy soul.
De:4:30:
When thou art in tribulation,
and all these things are come upon thee,
even in the latter days,
if thou turn to the LORD thy God,
and shalt be obedient unto his voice;
De:4:31:
(For the LORD thy God is a merciful God
he will not forsake thee,
neither destroy thee,
nor forget the covenant of thy fathers which he sware unto them.
You are right, it is complex in that the information is scattered about in all the text, the only hard part is finding all the relevant words, once you have 'most' (in that you might still be missing a few references) the understanding of what those words mean is quite easy to understand.
Isa:28:9:
Whom shall he teach knowledge?
and whom shall he make to understand doctrine?
them that are weaned from the milk,
and drawn from the breasts.
Isa:28:10:
For precept must be upon precept,
precept upon precept;
line upon line,
line upon line;
here a little,
and there a little:
It is so inconsistent on so many things, and makes so many readily falsifiable empirical claims, that I find it impossible to consider it as anything but the work of fallible human beings, not a revelation from any deity.
When I find something that 'seems' inconsistent it's a reason to do some more reading, assuming that it is my understanding that is in error and not His written word. Sooner or later I can usually find more info on the subject in question. A few quick examples, in Ezekiel 39 it says all Israel will die by the sword by the time the feast for the beasts of the field is 'ready'. Zechariah points to 1/3 of a group not dieing at His return. This is either a conflict of facts or it is simple referencing two different groups, Israel and Gentiles.
Another example is who is the rider in the vision that goes with the 1st seal. Most relate it to the last anti-christ, given authority to start the tribulation associated with Satan. They can't come up with any reference from Scripture that explains the bow he carries, they just kind of ignore that little part or point out that it is only a bow that is mentioned but no arrows are mentioned so there is a 'lack of real power'. If you take this Scripture into account does it a) add information b)identify the roder.
Isa:49:2:
And he hath made my mouth like a sharp sword;
in the shadow of his hand hath he hid me,
and made me a polished shaft; in his quiver hath he hid me;
That would certainly change who the rider was from being the anti-christ to it being God and the white horse being the Holy Spirit? That isn't inconsistent with other passages that says the end of times starts when God alone determines it actually starts. (Scripture does give a sequence of events and a time-line that precedes Christ's actual return).
Later