Jeremiah 31:33

"But this is the covenant that I will make with the house of Israel after those days, saith Jehovah: I will put my law in their inward parts, and in their heart will I write it; and I will be their God, and they shall be my people."

Notice that God does not here state that he will cancel or no longer require his law to be observed, but that he will achieve the observance of his holy law by an utterly new method. That new method would be by the means of "the new birth" (John 1:3-7). A new heart would be created in obedient believers, and this would enable a more acceptable obedience to Divine Law. God never envisioned a time when his followers (even Christians) would be able to achieve perfect obedience; and therefore in the great injunction for Christians to pray, one finds the words, "Forgive us our sins, as we forgive those who transgress against us."

Nevertheless, the requirement of holiness is nowhere eliminated or cancelled in the New Testament, but the Lord specifically declared that, "Without holiness, no man shall see God" (Hebrews 12:14).