There's a lot of people working for God, but not all of them are letting God work through them. Sounds like a condradictory statement, doesn't it? But actually it's not; working for God and God working through you can be two completely different things!
Wanting to work for God is a good thing. The Bible says that faith without works is dead, being alone. The Bible also says that we were saved to do good works and loving God makes you want to be about his business. But we can't forget that we are tools. God works through us just like we work through our tools. We wouldn't expect a hammer to start driving a nail all by itself! We use the tool to do the work we want done. The tool avails itself to us to be used and we decide what job to do and when and where to do it! Yes, the tool is working, in the sense that work is being done and the tool is invovled. But the actual power to get the work done and the knowledge about how to do the work is being supplied by us, not the tool! We are God's tools!
Many times, albeit with good intentions, we abandon our role as tools and decide to work for God on our own. We decide that a particular thing needs to be done, we decide it needs to be done now, we decide it needs to be done this way and then we set about doing it. When things don't work out like we expected, we wonder why God didn't make it work out, since we were doing it all for him in the first place! God backs his own plans, not ours! When he tells us to do something, he always provides the power and ability to do it. But he is not obligated to help us do what we want to do.
We need to make sure that what we are working at is something that God has told us (either in prayer or in his word) that he wants us to do. That way, we can be sure to have his help in getting it done and what we do will always be effective.