The beginning of James 5 is a little hard to mull over. I'll admit, this kind of stuff isn't necessarily my favorite to read. But it's there for a reason.
James is speaking specifically to a certain group in the early church when he writes this:
Come now, you rich, weep and howl for the miseries that are coming upon you. Your riches have rotted and your garments are moth-eaten. Your gold and silver have corroded, and their corrosion will be evidence against you and will eat your flesh like fire. You have laid up treasure in the last days. Behold, the wages of the laborers who mowed your fields, which you kept back by fraud, are crying out against you, and the cries of the harvesters have reached the ears of the Lord of hosts. You have lived on the earth in luxury and in self-indulgence. You have fattened your hearts in a day of slaughter. You have condemned and murdered the righteous person. He does not resist you.
-James 5:1-6 ESV
The problem with the rich people here was they valued things over God. They placed value on earthly things, things that wouldn't stick around forever. Things that were already rotting and decaying. Their church life may have been awesome, but God wants more than that.
When we got saved, we surrendered our whole life over to God. We have slowly began to take parts back, saying, "God, I want that," or, "God, you can't do that." We don't allow God to change us in such a radical way that it affects every aspect of our life! We don't experience that "new creation" feeling. God doesn't want a percentage of your life, He wants the whole thing! We're boxing God up and replacing Him with something else.
We have to allow God in all areas of our life or we will start to act like these hoarders and value and store up worthless junk instead of pursuing a fulfilling relationship with God.