The human tendency is to create religion as a framework for manipulating God and man. Historically, religious organizations (or even political organizations) have exploited their “close” association with the gods to provide them with financial riches, political strength, or social standing. When this is not the case, religion usually provides a framework by which men can do the right things to garner the blessing of a god/gods. Religion is really about man using gods for his own means.

Christianity is not that way.

From the days of walking in the Garden with Adam to the Incarnation of Christ, and right up to the present, God has always been interested in relating to mankind. Amos 4:13 describes him:

He who forms the mountains, creates the wind, and reveals his thoughts to man, he who turns dawn to darkness, and treads the high places of the earth — the LORD God Almighty is his name.

Many look at the sacrificial system laid out in the Old Testament as a giant set of rules for making God happy, but really they were only intended as a temporary means by which the Israelites could obey God, see his character, become more like him, offer payment of blood to temporarily turn aside God’s wrath over their continually rebellious ways, and be reminded that they can never satisfy God’s requirements on their own. Hebrews 10 tells us that

The law is only a shadow of the good things that are coming—not the realities themselves…but those sacrifices are an annual reminder of sins, because it is impossible for the blood of bulls and goats to take away sins.

Which brings me back to the place where this whole discourse came from: Psalm 51 beautifully demonstrates that David (or the Davidic character, long story!) already knew, long before Christ, that religion could never satisfy and manipulate God. He understood that what God wanted was a holistic relationship, the sacrifice of a life turned over fully to knowing and modeling God’s character. He writes:

You do not delight in sacrifice, or I would bring it;
      you do not take pleasure in burnt offerings.
The sacrifices of God are a broken spirit;
      a broken and contrite heart,
      O God, you will not despise.

If you are trying to obey and please God for your own gain (so he will answer your prayers and give you that new car!), if you repent merely to turn away his wrath, you’re engaged in religion. The actions may be different (prayer vs. sacrifice, volunteering vs. tithing) but the idea is the same: you’re in it for your own benefit. What God wants is you, He wants you to know and emulate Him. When you sin, he wants your heart to break over the violation of his character and love, not a ritualistic action to make it all better.

Israel had the sacrificial system when Psalm 51, but the author understands the God has never wanted religion. He has always desired an earnest, living, vibrant relationship with the people He was pleased to call his own.