Really, as Hebrews 8:8 says, the fault lay in the people who failed to keep the covenant. Their failure had provided much of the theme of Jeremiah. God had been like a faithful husband to the Israelites (Israel and Judah), but they became immoral and continually violated the covenant (Jeremiah 3:6-10; 11:10).
For He finds fault with them when He says: “Behold, the days are coming, declares the Lord, when I will establish a new covenant…. For they did not continue in My covenant.” (Hebrews 8:8, 9)
This was not a sudden impulse on the part of God. He had been extremely patient, generation after generation. From the beginning, He had warned of the consequences of breaking the covenant. The fault was not in God. The fault was in the people. Yet therein was the great problem: The Old Covenant had strict laws and punishments that condemned failure in its people. What God wanted and ultimately planned was to save people, not condemn them. For that He planned a New Covenant where His people would truly know Him (Hebrews 8:10-11), and where their faults would be forgiven and forgotten forever (Hebrews 8:12).