Because of this;
Romans 9:6-8, "However, it is not as though YHWH's plan had failed. For it is not everyone who is a descendant of Yisra’yl who belongs to Yisra’yl. Nor, just because they are his descendants, are they all Abraham's children; but: In Isaac will your seed be called. That is, it is not those who are the children of the flesh who are YHWH's children; but it is the children of the promise who are regarded as Abraham's seed."
Psalm 105:6-9, "O seed of Abraham His servant, You children of Yaaqob, His chosen ones! He is YHWH our Father! His judgments are in all the earth. He has remembered His covenant forever, the Law He commanded for a thousand generations; Which He made; ratified, established, with Abraham, and vowed by His oath to Isaac. He confirmed it; let it stand, to Yaaqob for a Law, and to Israyl for an everlasting covenant."
Galatians 3:27-29, “For as many of you as were immersed into Messiah have put on Messiah. There is not Yehuḏi nor Greek, there is not slave nor free, there is not male and female, for you are all one in Messiah יהושע. And if you are of Messiah, then you are seed of Aḇraham, and heirs according to promise.”
I believe that yes Yah spoke it to Abraham, but all the follow Yah in truth are a part of this Covenant/agreement/promise. It is also my beliefe that Yah gave man kind a single Covenant, He may have shown different elements of it at different times and to different peolpe, but He knows the end from the beginning and thue never had to alter things or change His plan. I believe this is shown here;
Psalm 89:26-37, "He will call out to Me; ‘You are my Father, O YHWH! You are the Rock of my salvation!’ And I will make Him My firstborn, higher than the kings of the earth. My mercy I will keep for Him forever and My covenant will stand fast withHim. And I will establish His Seed forever, and His throne will be as the days of heaven. Should His children forsake My Law, and refuse to walk in My judgments; Should they profane My statutes, and fail to keep My commandments; Then I will punish their transgression with the rod, and their iniquity with lashes from the whip. Nevertheless, My lovingkindness I will not utterly withdraw from Him, nor will I ever betray My faithfulness. My covenant I will not break, nor will I change what has gone out of My lips. Once for all, I have vowed by My holiness, I cannot lie, and I say to David; His Seed will endure forever, and his throne will endure before Me like the sun. His throne will be established forever like the moon: the faithful witness in the sky."
With that said, yes I believe the 2 greatest/10/613 Commandments still stand, but under Yahshua the High Priset not the Levites of course. and Yahshua taught the proper way to walk in them, the pharisees were evil and made their own law that for them circumvented Yah's Law every step of the way, while at the same time adding thousands of man made regulations that the lay people thought they had to keep.
So to sum it up, yes I believe the Law from the OT is what is summed up in the greatest Commandments;
Mat 22:37-40, "Yahshua said to him: You must love YHWH your Father with all your heart, and with all your soul, and with all your might. (Deut 6:5) This is the first and greatest commandment. And the second is like it: You shall love your neighbor as yourself. (Lev 19:18) On these two commandments hang all the Law and the Prophets."
“all” is word #G3650 - holos - Strong's Concordance, holos: whole, complete, Original Word: ὅλος, η, ον, Part of Speech: Adjective, Transliteration: holos, Phonetic Spelling: (hol'-os), Short Definition: all, the whole, entire, Definition: all, the whole, entire, complete
Matt 5:18, "For truly I say to you; Unless heaven and earth passes away, one yodh--the smallest of the letters--will in no way pass from the Law, until all things are perfected."
Revelation 21:1-2, "And I saw a new heaven and a new earth, for the first heaven and the first earth had passed away, and there was no more sea. And I, Yahanan, saw the holy city, YHWH Shammah, coming down from YHWH out of heaven, prepared as brides adorned for their husbands. And I heard a great voice out of heaven, saying: Behold, the tabernacle of YHWH is with men, and He will dwell with them, and they will be His people, and YHWH Himself will be with them, and be their Father.”
1 John 2:3-7, “And by this we know that we know Him, if we guard His commands. The one who says, “I know Him,” and does not guard His commands, is a liar, and the truth is not in him. But whoever guards His Word, truly the love of Yah has been perfected in him. By this we know that we are in Him. The one who says he stays in Him ought himself also to walk, even as He walked. Beloved, I write no fresh command to you, but an old command which you have had from the beginning. The old command is the Word which you heard from the beginning.”