Shaykh Yasir Qadhi talks about two topics - the wisdom behind a delayed response and the relationship of Dua with Qadr.
Every Dua is responded to and as opposed to what we normally assume.
Some wisdom behind a delayed response are as follows:
Allah is the Malik.
Man does not have a right over his Creator.
A delay in response is a trial.
Allah is the Most Wise.
The matter might bring evil.
Allah’s Choice is better than the choice of the servant.
Man does not know the result of his Dua.
Trials bring one closer to Allah.
Dua is the means that one uses to achieve the desired goals that one has, and this means in no way contradicts the destiny that has been written for that person. Divine Decree or Qadr cannot be made as an excuse to not make Dua. Dua is intrinsically related to Qadr so much so that it is a part of Qadr.