Tirmidhi

Explanation:
1:
By "qada" is meant the decreed matter (amr muqaddar).
Some people say:
The meaning is that supplication (dua) is extremely effective in averting calamity and misfortune,
to the extent that if it were possible for qada to be turned back by anything, it would be by supplication.
Whereas some people say:
What is meant is that supplication makes qada easy and light, so that it is as if the one making supplication feels that the qada did not descend at all.
This is also supported by the narration of Tirmidhi, in which supplication is proven to be beneficial for whatever qada has already descended and for what has not yet descended.

2:
If the increase in lifespan is in reality, then its meaning is that this increase is according to the knowledge of the angel who is appointed over the lifespan of a person,
not in relation to the knowledge of Allah,
for example, if it is recorded in the Preserved Tablet (al-Lawh al-Mahfuz) that so-and-so’s lifespan will be sixty years if he performs Hajj and Umrah, and forty years if he does not perform Hajj and Umrah, then it is in Allah’s knowledge whether he will perform Hajj and Umrah or not,
and there can be no alteration or change in the divine knowledge,
whereas in the knowledge of the angel, there is the possibility of change.