Ps 68 1 May God arise, may his enemies be scattered;
may his foes flee before him.
2 As smoke is blown away by the wind,
may you blow them away;
as wax melts before the fire,
may the wicked perish before God.
3 But may the righteous be glad
and rejoice before God;
may they be happy and joyful."

The Psalms are spoken about the earth and the events of time from Gods view point. It is a book that teaches us that God lowers Himself to our level and speaks according to His view. You cannot assume that the expressions of the normal way that we communicate with one another are the only ones. This is what is confusing to people who have never prayed the Psalms. The normal person who has a knowledge of the Psalms but does not pray them does not understand that the Psalms are contained within themselves. In other words the terrible expressions in the Psalms are there for the people of God to develop in a relationship with the Father and not through meeting the requirements in order to develop the relationship.You see we were made like God and the Psalms teach us that as we think and desire like God , that unity that is developed comes through a growing freedom in which the fellowship is in the contained pronouncements of the Psalms expressed in unity with our Fathers desires.
So we find two extremes expressed side by side with each other. The reason that the Psalms express extreme anger and the highest joy is because we are always motivated in whatever circumstance that we are face by the understanding that God can change everything in our lives by speaking one word. We are never motivated by anything that opposes us. There are many things like pain, people, corruption, sin etc. The Psalms teach that all opposition must be opposed by Gods word. In other words the opposition pushing us in the opposite direction of our desires. We oppose all opposition through Gods pronounced words. We never think of any opposition according to our experience or according to our view of the power of that opposition. We wrestle with opposition as it is defined in the time we oppose it in the pronouncements. One pronouncement leads us to another pronouncement until we are satisfied that we will overcome. This is what is being taught here..i will further explain.