Examples from Scripture that refute the notion that God's Law as given to Moses and explained in the case laws in the Old Testament is not valid anymore:

• Keeping the Passover is an everlasting ordinance: Exo 12:14.
• The Ten Commandments are to be kept throughout the generations, for God is a jealous God and will show mercy to those that keep His commandments into the thousands generation, but if you work iniquity, it will be held against you and your family for up to four generations: Exo 20 and Deu 5.
• You are defiling yourself or the land by things abominable to the Lord, by lawlessness: Lev 18.
• There is severe punishment for changing the ordinance and breaking the covenant: Isa 24.
• Jesus enforces the Law:

"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." (Mat 5:18)

• John stresses that the Law has been unchanged from the beginning in his 2nd letter:

"And now I beseech thee, lady, not as though I wrote a new commandment unto thee, but that which we had from the beginning, that we love one another. And this is love, that we walk after his commandments. This is the commandment, That, as ye have heard from the beginning, ye should walk in it." (2 Jn 1:5-6).

Read on here:

Obstacle #1: God's Law Is Done Away With Part 2

When it comes to the Scriptures, Mark Twain's remark applies in an interesting way:

"It is not what you do not know that will hurt you the most. It is what you think you know, but it just ain’t so!"