When response to our du’a is delayed, this is a type of test and trial that is inflicted upon a servant. This necessitates being patient during a trial. So a person should realise that, just like our entire life is a trial and a test for us, so too is this delayed response. This is just one of the many trials that we must face if we eventually wish to enter Paradise and please our Creator.
As Allah says:
“And we test you, with good and evil, as a fitnah. And to Us you will return.” (Surah al-Anbiya:35)
We can see that both good and evil are a trial or fitnah for us, to see whether we are patient when afflicted by evil, and whether we use the good we have been given properly.