"because Abraham obeyed my voice and kept my charge, my commandments, and my laws." (Genesis 26:5) OT
"Yet the house of Israel rebelled against Me in the wilderness. They did not follow My statutes and they rejected My ordinances" (Ezekiel 20:13) OT
*Joseph knew it was a sin to Commet adultery. (Gen 39:9) OT
"In whom the god of this world hath blinded the minds of them which believe not, lest the light of the glorious gospel of Christ, who is the image of God, should shine unto them.” (2 Cor 4:4) OT
"15 See, I have set before thee this day life and good, and death and evil;
16 In that I command thee this day to love the Lord thy God, to walk in his ways, and to keep his commandments and his statutes and his judgments...," (Deuteronomy 30:15-20) OT
"And I will put my spirit within you, and cause you to walk in my statutes, and ye shall keep my judgments, and do them." (Ezekiel 36:27)
there are more.
Now don't just respond to these answers above, but as I answered your question answer mine.
Q: just explain the existence of the Ten Commandments and the Sabbath in the NT?
Blessings, Danny