But Paul treats them all as if they were manure, absolutely useless. Now listen, vice...listen carefully, vice is not the only muck of life. Vice is not the only useless refuse. Vice is not the only garbage. Vice is not the only rubbish. Religion is rubbish, too. Any man-made effort to gain salvation is as much rubbish as vice is rubbish. And Paul is speaking out of personal experience. He said that Christ saved him and he said, "I was the chief of sinners." And listen, he was the chief of sinners not because he lived a vice-filled lewd licentious life because he didn't, he lived an eminently moral life. But he saw the deepest vilest rubbish of life as religion...not immorality. It's one thing to act immorally, it's something else to believe that God is so low that you can earn acceptance with Him. One desecrates God to one degree, the other desecrates God to a greater degree. One violates His law, immorality, one assumes Him to be less than He is and violates His nature. Thus religion is a rubbish. And the rubbish that Paul viewed in his own life was not the rubbish of vice, but it was the rubbish of religion...of trying to please God through self-effort and religious works.
[Paul says] that true Christians put no confidence in the flesh. True Christians do not trust in anything they do to earn salvation. They put no confidence, zero confidence in the flesh. True Christians, those who have the true circumcision, which is a spiritual circumcision, they worship in the Spirit of God, ...and their joy and their glory and their boasting is all in Christ Jesus and they put no confidence in the flesh...none whatsoever. The flesh provides nothing even when it acts religiously. There are people, plenty of them, the world is filled with them, who live under the deceptive illusion that they can work their way to God, that by religious duty and ceremony and all of that they can earn their way into God's presence. They can acquire the privilege of eternal life. That's confidence in the flesh. Paul says true believers have none of it. Paul wants none of that illusion.
(Excerpted from "Religious Credits that Don't Impress God" from the sermon series "The Road to Nowhere" by John MacArthur http://www.gty.org/resources/sermons/50-31/religious-credits-that-dont-impress-god)