Tim Keller uses the following scenario to illustrate how we can sometimes love God just for the good stuff he's "supposed" to give us (based on our terms, of course), rather than loving God for God's sake. Keller writes:

Imagine being in a situation where you were dating somebody and you seemed to be falling in love. As part of getting to know one another, you let it be known that when you got married you were coming into a significant trust fund. The person who you're falling in love with said, "Oh, really? Well, it doesn't make any difference to me whether you're rich or poor. I love you for who you are."

Suppose, just before the wedding you learned that you weren't going to get that trust fund? When you relayed that to your spouse-to-be, he or she got so disappointed that they called off the wedding. How would you feel? What would that tell you about this person's love for you? What would you say? You would start to say, "You never loved me for me. You were using me. You loved me because I was going to get you somewhere or get you something. You didn't love me. You were using me."

Possible Preaching Angles: Instead of loving the Lord for who he is, we love him for what we believe he should give us right now (instead of waiting for our the promised "eternal weight of glory"). But when we realize we're not getting the trust fund that we think should come right now, we're ready to walk away. Sometimes the trials of life reveal the true nature of our faith. Sometimes we see that we are not serving God, we are using him!