The Psalmist is teaching that we can approach God when we are angry. The question is it good for saints to have a general attitude of anger as a result of being miss treated in the world?Should we be more concerned for examining our sin or see the importance of dealing with our anger on a daily basis?
The Psalmist starts the Psalms teaching us the entire world is in eternal darkness, and the sacred word remain the exclusive means to illuminate our way. In Psalm 2 , he teaches Gods judgements are not delayed. God is absolutely justified at all considerable times. His abundant blessing and hearty curses cannot be thwarted. Gods line of divine justice is always the same. Psalm 3 he carefully instructs us that we will typically encounter an insurmountable army as we live from day to day.He is teaching we should not be surprise when we look at the unique circumstances in our lives and feel like we are encountering an organized opposition as we were primed for war. The opposition we face made us fear for our lives. Then here in Psalm 4 he is teaching us that we live vicariously in a criminal world in which men scheme against Gods creative order. We are inevitably facing the miss representation of our plans to do good. We are always being forced in an evil prophecy about us and our purposes. It is fascinating the Psalmist carefully directs us how to adequately deal with our anger before Psalm 5 in how to deal with our moral guilt.

 Hence, we see in the opening of the Psalms he is showing that we must approach God throughout every day in order to deal with personal attitudes. We cannot allow these attitudes of sloth, lack of faith, having no hope, being hardened by anger and guilt to flourish from one day to the next. We must carefully apply these Psalms so that we will not allow ourselves to be hardened. In this Psalm he is demonstrating  the unique importance of knowing the evil scheme that we are always facing and rolling over to God.
In Psalm 2 we are directed that the world is controlled by Gods kingdom principles. Man cannot opposes the eternal kingdom of God because God accurately judges all things in eternal life and death pronouncements. In this Psalm God is the Elohim create the re ordering of all things and has revealed them in Christ. When we are saved, we are set apart from the world by grace. In Psalm 3 he describes our considerable opposition in the world, but in 4 he is uniquely describing our inward opposition. He is saying that all communication endure a war between a world where man returns to his primary purpose of enjoying the gifts of God. God is reordering our comprehensive view by teaching us the divine prophecy of blessing. But wicked men devise schemes that oppose our view of a righteous God. He is instructing us that we must discern the elaborate schemes and be aware of our possible reaction of anger in resolutely facing the organized opposition. We must deal with our passionate anger before it hardens us.

We approach God with the law, covenants, curses, etc. on our lips. Offer right sacrifices and trust in the Lord. Here trusting is "confiding in" so as to be secure. Gods word undoubtedly constitutes the reasonable basis of our trust as we speak the generous gifts. When the Psalmist graciously offers a sacrifice, he is carefully approaching God graciously according to his present disposition. The Psalmist sacrifices with a overflowing joy, and enlarged view of God, a humble confession in an eternal covenant, when he is in imminent danger, and in this Psalm he is properly dealing with anger. This is a picture of substitution by death. It pleased God to justly punish Christ who quelled all corrupt opposition. The substitutionary work of Christ is that by which we can role all our troubles both inward and outward over to God.