Come, let us sing for joy to the LORD; let us shout aloud to the Rock of our salvation. Let us come before him with thanksgiving and extol him with music and song.  For the LORD is the great God, the great King above all gods. In his hand are the depths of the earth, and the mountain peaks belong to him.  The sea is his, for he made it, and his hands formed the dry land.  Come, let us bow down in worship, let us kneel before the LORD our Maker; for he is our God and we are the people of his pasture, the flock under his care.

Today, if you hear his voice, do not harden your hearts as you did at Meribah, as you did that day at Massah in the desert, where your fathers tested and tried me, though they had seen what I did. For forty years I was angry with that generation; I said, "They are a people whose hearts go astray, and they have not known my ways."  So I declared on oath in my anger, "They shall never enter my rest."

This psalm was just spewing out it's praise to GOD in the first half. But when it reaches about the half line, they go WAY  off course! Why did they mean? why were they even talking about that? What did it have too do with anything?