When our du’a is apparently not answered, it causes us to contemplate our lives and the good and the bad thereof. It causes us to examine our du’a and why we are making it. It causes us to examine our life and what we want from it. It causes us to examine our money, and how we are earning it and spending it. And it causes us to examine our good deeds, and how good they actually are. It will also make us look at our evil deeds and see how numerous they are. This will in turn cause us to turn to Allah in repentance, and to change our ways. Know that these effects can only occur with a true believer.
We can see therefore that this delay in response is actually a cleansing experience and a purification for the Muslim. It forces us to re-exmine our relationship with Allah, and to try and strengthen it. Had our du’a been immediately responded to, this examination would not have taken place, nor would any extra good have come from it. So because of the delay, and person finds themselves and examines themselves, and this, in and of itself, is a blessing from Allah, all praises and glory be to Him.