"This is what the Lord says: 'What fault did your fathers find in me, that they strayed so far from me? They followed worthless idols and became worthless themselves.'" NIV translation
God asks the people for the reason that they turned their back on Him. This question was meant to get them to see how ridiculous it is to turn from Him and embrace worthless (dead) things. The simple answer is that there is no fault with God.
"'They did not ask, "Where is the Lord, who brought us up out of Egypt and led us through the barren wilderness, through a land of deserts and rifts, a land of drought and darkness, a land where no one travels and no one lives?"'" NIV translation
When times were tough and they had to go through struggles, the people clung to God and followed Him wholeheartedly. As time went by and it was forgotten (and not taught to the children) the people felt as if they did not need God. Then, when the tough times came again, they turned to any and all idols to help them.
Many of us do the same things today as we have forgotten how God has delivered us out of our sin. This leads us to trust in our own efforts, our bank accounts, or other things and we get further and further away from God. During the smooth times, we need to remember how God has delivered us from the rough times. This will prepare us for the trials and troubles that are to come. A big part of remembering is sharing your testimony with others.
"'I brought you into a fertile land to eat its fruit and rich produce. But you came and defiled my land and made my inheritance detestable.'" NIV translation
The people forgot that God was their provider and that He had given them this wonderful land. They turned to worship things that they had made with their own hands and so even the land became detestable to God. This verse can also remind us that God does not want to only deliver us through the tough times but He also wants to richly provide for our needs.