Psalm 76

We will not hide them from their children; we will tell the next generation the praiseworthy deeds of the LORD, his power, and the wonders he has done. He decreed statutes for Jacob and established the law in Israel, which he commanded our forefathers to teach their children,  so the next generation would know them, even the children yet to be born, and they in turn would tell their children. Then they would put their trust in God and would not forget his deeds but would keep his commands. They would not be like their forefathers— a stubborn and rebellious generation, whose hearts were not loyal to God, whose spirits were not faithful to him. The men of Ephraim, though armed with bows, turned back on the day of battle;  they did not keep God's covenant and refused to live by his law. They forgot what he had done, the wonders he had shown them.


Ephraim forgot what God did for them, and the next thirty verses are what they forgot.
 
Again and again they put God to the test; they vexed the Holy One of Israel
 
How could you forget the whole story of how God brought your forefathers out of egypt?  I mean, that's practicly immpossible!
 
Then he rejected the tents of Joseph, he did not choose the tribe of Ephraim; but he chose the tribe of Judah, Mount Zion, which he loved. He built his sanctuary like the heights, like the earth that he established forever.  He chose David his servant and took him from the sheep pens; from tending the sheep he brought him to be the shepherd of his people Jacob, of Israel his inheritance. And David shepherded them with integrity of heart; with skillful hands he led them.
 
But since they forgot so bad, they completely sinned against God, so God didn't choose them. That's why it's so important to teach children the word of God!